










LC REGUT, A 
OR REP 
DOCtP 

MARK 


t>t~ "IE SERVICING 
'ART OF THIS 
ICATION 
2 AJCELLED. 


«3 


ts 8? 

€ B a 

c ; 2 § 

• br. «- 

S <• o 

> UM >s 
- *- ■ 1 S3 

r,i 5 


Sag 


Ssg 

SKI 


RECLASSIFIED 
By authority Secretary of 


SFP 1 1960 
Defense memo 2 August I960 
LIBRARY OF CONGRESS 












/a 


a ^sr 

a $> 



*$y a ;%."•• /f* 

& ch^^s* 


^ /S v>- ryr 

; 4' 

^ A 


A/v 

;Fy> 


^ ; V ^ 






I 



SUMMARY TECHNICAL REPORT 


OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 


This document contains information affecting the national defense of 
the United States within the meaning of the Espionage Act, 50 U. S. C., 
31 and 32, as amended. Its transmission or the revelation of its con- 
tents in any manner to an unauthorized person is prohibited by law. 

This volume is classified^^^|^^B in accordance with security regu- 
lations of the War and N av^^ ^part ments because certain chapters 
contain material which was (SEGSH at the date of printing. Other 
chapters may have had a low^WBIBfication or none. The reader is 
advised to consult the War and Navy agencies listed on the reverse 
of this page for the current classification of any material. 


Manuscript and illustrations for this volume were prepared 
for publication by the Summary Reports Group of the 
Columbia University Division of War Research under con- 
tract OEMsr-1131 with the Office of Scientific Research and 
Development. This volume was printed and bound by the 
Columbia University Press. 

Distribution of the Summary Technical Report of NDRC 
has been made by the War and Navy Departments. Inquiries 
concerning the availability and distribution of the Summary 
Technical Report volumes and microfilmed and other refer- 
ence material should be addressed to the War Department 
Library, Room 1A-522, The Pentagon, Washington 25, D. C., 
or to the Office of Naval Research, Navy Department, Atten- 
tion : Reports and Documents Section, Washington 25, D. C. 


Copy No. 

119 


This volume, like the seventy others of the Summary Tech- 
nical Report of NDRC, has been written, edited, and printed 
under great pressure. Inevitably there are errors which have 
slipped past Division readers and proofreaders. There may 
be errors of fact not known at time of printing. The author 
has not been able to follow through his writing to the final 
page proof. 

Please report errors to : 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports 
and sent to recipients of the volume. Your help will make 
this book more useful to other readers and will be of great 
value in preparing any revisions. 


SUMMARY TECHNICAL REPORT OF DIVISION 4, NDRC 


VOLUME 1 


RADIO PROXIMITY FUZES 
FOR FIN-STABILIZED 
MISSILES 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 
VANNEVAR BUSH, DIRECTOR 

NATIONAL DEFENSE RESEARCH COMMITTEE 
JAMES B. CONANT, CHAIRMAN 

DIVISION 4 

ALEXANDER ELLETT, CHIEF 


WASHINGTON, D. C., 1946 


RET 


NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative 1 

Frank B. Jewett Navy Representative 2 

Karl T. Compton Commissioner of Patents 3 

Irvin Stewart, Executive Secretary 


1 Army representatives in order of service : 


Maj. Gen. G. V. Strong 
Maj. Gen. R. C. Moore 
Maj. Gen. C. C. Williams 
Brig. Gen. W. A. Wood, Jr. 

Col. E. A. 


Col. L. A. Denson 
Col. P. R. Faymonville 
Brig. Gen. E. A. Regnier 
Col. M. M. Irvine 
Routheau 


2 Navy representatives in order of service : 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 
Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 
Commodore H. A. Schade 

3 Commissioners of Patents in order of service : 
Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suit- 
able projects and research programs on the instru- 
mentalities of warfare, together with contract facilities 
for carrying out these projects and programs, and (2) 
to administer the technical and scientific work of the 
contracts. More specifically, NDRC functioned by initi- 
ating research projects on requests from the Army or 
the Navy, or on requests from an allied government 
transmitted through the Liaison Office of OSRD, or on 
its own considered initiative as a result of the expe- 
rience of its members. Proposals prepared by the Divi- 
sion, Panel, or Committee for research contracts for 
performance of the work involved in such projects were 
first reviewed by NDRC, and if approved, recommended 
to the Director of OSRD. Upon approval of a proposal 
by the Director, a contract permitting maximum flexi- 
bility of scientific effort was arranged. The business 
aspects of the contract, including such matters as mate- 
rials, clearances, vouchers, patents, priorities, legal 
matters, and administration of patent matters were 
handled by the Executive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 

These were: 

Division A — Armor and Ordnance 
Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three 
administrative divisions, panels, or committees were 
created, each with a chief selected on the basis of his 
outstanding work in the particular field. The NDRC 
members then became a* reviewing and advisory group 
to the Director of OSRD. The final organization was as 
follows : 

Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub-Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


Library of Congress 



201 5 490929 


iv 



NDRC FOREWORD 


A S events of the years preceding 1940 re- 
vealed more and more clearly the serious- 
ness of the world situation, many scientists in 
this country came to realize the need of organ- 
izing scientific research for service in a national 
emergency. Recommendations which they made 
to the White House were given careful and 
sympathetic attention, and as a result the Na- 
tional Defense Research Committee [NDRC] 
was formed by Executive Order of the Presi- 
dent in the summer of 1940. The members of 
NDRC, appointed by the President, were in- 
structed to supplement the work of the Army 
and the Navy in the development of the instru- 
mentalities of war. A year later, upon the estab- 
lishment of the Office of Scientific Research and 
Development [OSRD], NDRC became one of 
its units. 

The Summary Technical Report of NDRC is 
a conscientious effort on the part of NDRC to 
summarize and evaluate its work and to present 
it in a useful and permanent form. It com- 
prises some seventy volumes broken into groups 
corresponding to the NDRC Divisions, Panels, 
and Committees. 

The Summary Technical Report of each Di- 
vision, Panel, or Committee is an integral sur- 
vey of the work of that group. The report of 
each group contains a summary of the report, 
stating the problems presented and the philos- 
ophy of attacking them, and summarizing the 
results of the research, development, and train- 
ing activities undertaken. Some volumes may be 
“state of the art” treatises covering subjects to 
which various research groups have contrib- 
uted information. Others may contain descrip- 
tions of devices developed in the laboratories. A 
master index of all these divisional, panel, and 
committee reports which together constitute the 
Summary Technical Report of NDRC is con- 
tained in a separate volume, which also includes 
the index of a microfilm record of pertinent 
technical laboratory reports and reference ma- 
terial. 

Some of the NDRC-sponsored researches 
which had been declassified by the end of 1945 
were of sufficient popular interest that it was 
found desirable to report them in the form of 
monographs, such as the series on radar by 
Division 14 and the monograph on sampling in- 
spection by the Applied Mathematics Panel. 
Since the material treated in them is not dupli- 
cated in the Summary Technical Report of 
NDRC, the monographs are an important part 


of the story of these aspects of NDRC research. 

In contrast to the information on radar, 
which is of widespread interest and much of 
which is released to the public, the research on 
subsurface warfare is largely classified and is 
of general interest to a more restricted group. 
As a consequence, the report of Division 6 is 
found almost entirely in its Summary Technical 
Report, which runs to over twenty volumes. The 
extent of the work of a Division cannot there- 
fore be judged solely by the number of volumes 
devoted to it in the Summary Technical Report 
of NDRC ; account must be taken of the mono- 
graphs and available reports published else- 
where. 

The program of Division 4 in the field of elec- 
tronic ordnance provides an excellent example 
of the manner in which research and develop- 
ment work by a civilian technical group can 
complement and supplement work done by the 
Armed Services. The greatest responsibility of 
Division 4, under the leadership of Alexander 
Ellett, was to undertake the development of 
proximity fuzes for nonrotating or fin-stabilized 
missiles, such as bombs, rockets, and mortar 
shells. 

Early work on fuzes of various types indi- 
cated that those operating through the use of 
electromagnetic waves offered the most promise ; 
the eventual device depended on the doppler 
effect, combining the transmitted and received 
signals to create a low frequency beat which 
triggered an electronic switch. During the last 
phases of the war against Japan, approximately 
one-third of all the bomb fuzes used by carrier- 
based aircraft were proximity fuzes. For im- 
proving the accuracy of bombing operations, 
the Division developed the toss bombing tech- 
nique, by which the effect of gravity on the 
flight path of the missile is estimated and 
allowed for. The success of this technique is 
demonstrated by its combat use, when a circle 
of probable error as low as 150 feet was 
obtained. 

The Summary Technical Report of Division 
4 was prepared under the direction of the Di- 
vision Chief and has been authorized by him for 
publication. We wish to pay tribute to the enter- 
prise and energy of the members of the Di- 
vision, who worked so devotedly for its success. 

Vannevar Bush, Director 
Office of Scientific Research and Development 
J. B. Conant, Chairman 
National Defense Research Committee 



FOREWORD 


T he primary program of Division 4, NDRC, 
was development of proximity fuzes for 
bombs, rockets, and trench mortar projectiles. 
The National Bureau of Standards [NBS] pro- 
vided facilities and personnel for the Division’s 
Central Laboratory and the Division (or its 
predecessor, Section E of Division A) served 
as the principal liaison between NDRC and 
NBS. In large measure the developments pre- 
sented in this Division 4 STR must be credited 
to the National Bureau of Standards. Credit 
also is due the Ordnance Department of the 
Army for excellent cooperation. The main- 
tenance of effective liaison was due largely to 
Colonel H. S. Morton, whose enthusiasm for 
the program coupled with intelligent criticism 
and suggestions based on sound technical 
knowledge contributed much of value. 

The present volume summarizes the Divi- 
sion’s development of radio proximity fuzes. 
The technical direction of this development was 
throughout in the able hands of Harry Dia- 
mond, leader of the little radio fuze group 
organized at the Bureau of Standards in De- 
cember 1940, and finally Chief of the Bureau’s 
Ordnance Development Division. Throughout 
the program, he received invaluable technical 
assistance from W. S. Hinman, Jr., Chief 
Engineer of the aforementioned NBS division. 
The excellent presentation found here is due 
to the editor of these three volumes, A. V. 
Astin, Assistant Chief of the Ordnance De- 
velopment Division, NBS. 


Other Division 4 contractors made valuable 
contributions to particular projects on which 
they were engaged. Deserving of special men- 
tion are the University of Florida for work on 
trench mortar fuzes, the Globe-Union Com- 
pany of Milwaukee for work on safety and 
arming devices and ceramic circuits, and the 
University of Iowa for improved recovery de- 
vices and a smooth working proof organization. 
The development of generator power supplies 
was largely carried out by the Westinghouse 
Company in Baltimore and by the Zenith Radio 
Corporation. 

Reliability of radio fuzes depends at least as 
much on good production methods and tech- 
niques as upon good design. In the solution of 
production problems outstanding contributions 
were made by the Zell Corporation, Baltimore, 
and Bowen and Company, Bethesda, Maryland, 
who operated pilot lines; and by the Arnold 
Engineering Company, the Emerson Radio and 
Phonograph Corporation, the General Electric 
Company, the Globe-Union Company, the 
Philco Corporation, the Raytheon Manufactur- 
ing Company, the Sylvania Electric Products, 
Inc., the Westinghouse Electric and Manufac- 
turing Company, the Rudolph Wurlitzer Com- 
pany, and the Zenith Radio Corporation, who 
produced fuzes or fuze components. 


Alexander Ellett 
Chief, Division 4 


SECRET 


vii 



PREFACE 


T he Summary Technical Report of Division 
4 has been prepared in three volumes : 
Volume 1, describing the work on radio prox- 
imity fuzes, the major work of the division; 
Volume 2, discussing bomb, rocket, and torpedo 
tossing, a new fire control method for airborne 
missiles; and Volume 3, a report on various 
miscellaneous projects. An overall summary of 
the Division 4 program appears as Chapter 1 in 
Volume 3. 

The present volume treats the technical prob- 
lems relating to the design, production, and use 
of radio proximity fuzes for fin-stabilized (non- 
rotating) missiles, including bombs, rockets, 
and trench mortar shells. For a treatment of 
work on fuzes for spin-stabilized projectiles, the 
reader is referred to the reports of Section T 
of OSRD. For work on other types of proximity 
fuzes for fin-stabilized missiles, the reader is 
referred to Volume 3 of the Division 4 STR. 
The latter reference includes a general survey 
of various types of proximity fuzes and a de- 
tailed summary of the work done by Division 4 
on photoelectric fuzes. 

A primary consideration in the preparation 
of this volume has been to arrange the material 
so that it will be useful for reference purposes. 
To fulfill this objective, the various chapters are 
reasonably self-contained, and each chapter 
may be read separately without too much loss 
in meaning. This mode of presentation has, of 
course, resulted in some duplication of ma- 
terial, but it is believed that the advantages 
justify the extra space required. Numerous 
cross references between the chapters are in- 
cluded to facilitate expansion or clarification of 
various items. 

For the reader who is interested primarily 
in the essential operating characteristics of the 
radio proximity fuzes placed in production, 
Chapter 5, “Catalogue of Fuze Types,” is the 
only part of this volume which need be read. 
The catalogue chapter also includes a descrip- 
tion of the important features of design for 
each of the various fuzes. 

The introduction to the volume (Chapter 1) 
explains the objectives of the development pro- 
gram, how radio fuzes operate, and includes a 


brief summary of the accomplishments in the 
development and production program. 

Chapter 2 discusses in detail the basic theory 
of operation and shows how the required 
operating characteristics of a fuze may be con- 
verted into an engineering design problem. The 
material of Chapter 2 is fundamental to any 
fuze design involving interaction of radio waves 
with the target. Because of the great potential 
use of this theory in future development work, 
the treatment of Chapter 2 is much more 
thorough than would appear necessary merely 
as a summary of completed work. 

The methods by which the electrical design 
problems were solved are discussed in Chapter 
3. Section 3.4 of Chapter 3 deals with the de- 
sign of generator power supplies, one of the 
outstanding features of the later fuzes de- 
veloped by Division 4. Although this section is 
included in the electrical design chapter, it 
contains considerable material relating to the 
mechanical design of generators. A clear-cut 
separation of the mechanical and electrical de- 
sign requirements for the generator was not 
practicable. Chapters 2 and 3 are quite technical 
in nature and will probably be of interest only 
to scientists and engineers. These chapters may 
be omitted by the nontechnical reader. 

Chapter 4 analyzes the problems of mechan- 
ical design and layout and includes a treatment 
of the arming and safety features of the 
fuzes. 

Chapter 6 describes the production methods 
and summarizes accomplishment in the produc- 
tion program. Since the problems of reducing a 
laboratory design of a proximity fuze to a model 
which could be built in mass production were 
fundamental to the entire program, the story 
of this chapter is of basic importance. It should 
be of interest to both the technical and the non- 
technical reader. 

Chapters 7 and 8 describe the methods of 
testing proximity fuzes in order that their 
quality might be evaluated and their perform- 
ance under operational conditions predicted. 
The former chapter is concerned with labora- 
tory test methods and quality control. A de- 
scription of testing apparatus is included. The 


IX 


X 


PREFACE 


latter chapter deals with field test methods and 
proving ground procedures in which opera- 
tional conditions were simulated. 

Chapter 9 gives a somewhat more detailed 
analysis of the operating characteristics of the 
fuzes than is given in Chapter 5 in that the 
results of all important tests which were car- 
ried out on the fuzes are summarized. The 
chapter includes evaluations of performance 
for each of the fuze types under a variety of 
operating conditions. The operational experi- 
ence is also presented in this chapter. 

An analysis of problems pertaining to 
countermeasures and counter-countermeasures 
has not been included in this volume. 

The successful development of radio prox- 
imity fuzes, or VT fuzes as they are commonly 
called, involved the cooperative efforts of many 
organizations and individuals. A listing of all 
of the individuals who contributed to the suc- 
cess of the program would be an extremely 
difficult, perhaps even impossible, task. How- 
ever, the organizations which participated in 
the development program are listed at the end 
of the volume. 

This volume was prepared by the staff of the 
Ordnance Development Division of the Na- 
tional Bureau of Standards, which served as 
the central laboratories for Division 4. Reports 
of the various contractors to Division 4 have 


been used freely, and these are listed as refer- 
ences in the bibliography. 

The editor wishes to take this opportunity to 
record thanks and appreciation for the efforts 
of the many individuals who cooperated in the 
preparation of the volume. In particular, some 
of these are: Dr. Robert D. Huntoon, who as- 
sisted in the overall planning of the volume and 
who was also the senior author of Chapter 2; 
Dr. Alexander Ellett and Mr. Harry Diamond, 
Chief, Division 4 and Chief, Ordnance Develop- 
ment Division, respectively, who offered valu- 
able suggestions and advice on numerous items ; 
other authors who are listed in the table of 
contents as well as in footnotes to the various 
sections which they prepared ; Mr. Theodore C. 
Hellmers, who prepared the photographs used 
in this volume (unless credit is otherwise in- 
dicated) ; Mr. E. W. Hunt and his staff for their 
diligent and painstaking efforts in the prepara- 
tion of other art work; Miss Lee Smolen and 
Mrs. Henrietta Leiner for preparation of 
bibliographical material; and Miss Helen Olm- 
stead, Mrs. Betty Hallman, and Miss Jane 
Grant for their untiring efforts in the prepara- 
tion, assembly, and correction of manuscripts. 


A. V. Astin 
E ditor 



CONTENTS 


CHAPTER PAGE 

1 Introduction 1 

2 The Radiation Interaction System 17 

3 Electronic Control Systems 81 

4 Mechanical Design 167 

5 Catalogue of Fuze Types 209 

6 Production 245 

7 Laboratory Testing of Fuzes 278 

8 Field Testing of Proximity Fuzes 312 

9 Analysis of Performance 360 

Glossary 433 

Bibliography 437 

OSRD Appointees 463 

Contract Numbers 464 

Service Project Numbers 467 

Index 469 



xi 



Strike photograph of the first operational use of proximity fuzed bombs. The target is the beach area of 
I wo Jima during the pre-invasion bombing of the island. The characteristic crescent-shaped fragmentation 
patterns of air-burst bombs are clearly recognizable. (Army Air Force photograph.) 


t,C RE'--' 
OR RT’" 
DOCTT 
MARK J 


rT BEFORE SERVICING 
T NG AM PART OF THIS 
V , C Ac T TCATION 
.iU3T BE _CA T3E ,LEDT 


Chapter 1 


INTRODUCTION 


LC REGULATION: BEFORE SERVICING 
OR REPRODUCING ANY PART OF THIS 
DOCUMENT, ALLjCLASSIFICATION 
MARKINGS MUST BE CANCELLED: 


1 * OBJECTIVES AND MILITARY 
REQUIREMENTS 

R adio proximity fuzes are intended to deto- 
nate missiles automatically upon approach 
to a target and at such a position along the 
flight path of the missile as to inflict maximum 
damage to the target. 

The optimum position for detonation of the 
missile depends upon the nature of the target 
and the properties of the missile. Conditions 
of use divide possible targets into two major 
groups: (1) airborne targets, and (2) surface 
targets either on the ground or on water. These 
two applications are referred to variously as 
(1) antiaircraft, air-to-air, ground-to-air, and 
(2) ground-approach, air burst, air-to-ground, 
ground-to-ground. 

As a class, proximity fuzes belong with time 
fuzes, in contrast with contact fuzes, since they 
are useful wherever contact of the missile with 
the target or penetration into the target is not 
necessary to inflict damage. Because of the au- 
tomatically accurate nature of their operation, 
proximity fuzes not only extensively replace 
time fuzes, but they make possible many new 
and important applications for which time fuzes 
would be ineffective. They also replace contact 
fuzes in many applications where contact with 
an object, not necessarily the target, is used 
merely as a triggering operation for the fuzes 
and not because contact is essential to inflict 
damage. 

Military requirements for proximity fuzes 
became specific and well defined only after the 
development had passed the exploratory stage. 
Initially the requirements were quite general; 
(1) the fuze should detonate the missile “in the 
vicinity” of the target, (2) the fuze should be 
as small and rugged as possible, (3) it should 
be safe for handling and operational use, (4) it 
should perform reliably under a wide range of 
service conditions, (5) it should require a mini- 
mum of special equipment and training for its 
operational use, (6) it should be relatively im- 
mune to possible enemy countermeasures, and 


(7) in antiaircraft weapons, it should have a 
self-destruction [SD] feature to operate, in case 
of a miss, after passing the target. Most of the 
foregoing requirements could not be more ac- 
curately specified until a certain amount of 
design experience was available or until actual 
fuzes were available for proving ground tests. 

For example, the careful definition of the 
proper point on the trajectory for the fuze to 
function had to be based on experimental trials 
using fuzes against actual or simulated targets. 
Before the fuzes could be built for such tests, 
estimates were required concerning the ex- 
pected optimum conditions. In the antiaircraft 
case, it was fairly obvious that the position of 
function should be matched to the dynamic frag- 
mentation pattern of the missile so that the 
greatest number of fragments would be di- 
rected at the target. To achieve the proper 
directional sensitivity, a number of factors, as 
shown in Chapters 2 and 3, had to be balanced 
against each other, and the final specification 
of performance was based on numerous design 
compromises and field tests. In the ground tar- 
get case, no experimentally verified optimum 
burst heights were available until the end of 
1944 and then only for limited types of missiles 
and targets/ For many important ground tar- 
get applications, optimum burst heights are still 
undetermined. 

Some of the mechanical features were capa- 
ble of more exact specification. Although small 
size and ruggedness were objectives toward 
which improvement was continuous, certain 
minimum requirements were definite very early 
in the program. Bomb fuzes were to be bal- 
listically interchangeable with regular fuzes so 
that their use would require no modifications 
in bombing tables. Available stowage space in 
bomb bays made it necessary to impose limita- 
tions on overall length, and a maximum exten- 
sion of 5 in. beyond the nose of the bomb was 
prescribed, although shorter fuzes were pre- 

a These statements refer specific al^~^ G tfie ^uzes fu r" 
fin -stabilized or nonrotating nB§Bila*lth<Mlit$s SftGM&fc^ry of 
rockets, and trench-mortar shells. 



SEP 1 196p 

Defense memo 2 August 1960 


LIBRARY OF CONGRESS 



2 


INTRODUCTION 


ferred. Standard fuze-well cavities in bombs 
fixed other dimensions. A minimum require- 
ment on ruggedness was that the fuze with- 
stand any vibrations or accelerations of the 
missile. There were also standard military 
rough-handling specifications but these were 
more of a requirement for packaging than for 
fuze design. 

The arming and safety requirements, with 
one important exception, had to be worked out 
experimentally as the development progressed. 
The exception was the specification for an inter- 
rupted powder train between the detonator and 
booster, a standard Army Ordnance technique 
which was required of all proximity fuzes. 
Since proximity fuzes are, by their very nature, 
susceptible to their surroundings and unable 
to distinguish between friendly and enemy tar- 
gets, the arming problem is appreciably differ- 
ent than with ordinary fuzes. In general, longer 
“safe” times after firing or release of the mis- 
sile are desired for proximity fuzes, but an 
ideal safe period compromises the usefulness of 
the weapon. The details of the development of 
the arming and safety features and require- 
ments are discussed in Chapter 4. 

The very necessary exploratory work on 
radio proximity fuzes, was done under rather 
general requests from the Services, including 
a conference on August 12, 1940, between rep- 
resentatives of the Navy Bureau of Ordnance 
and NDRC j 1 Projects OD-27, dated January 14, 
1941, and OD-3B, dated June 11, 1941, of the 
Army Ordnance Department; and Project 
CWS-19, dated August 30, 1941, from the 
Chemical Warfare Service. The pertinent mili- 
tary characteristics for fuzes covered by these 
authorizations were essentially as outlined. 

After laboratory development and field tests 
had established general possibilities and limits 
for radio proximity fuzes, specific Service re- 
quirements were put forth based on anticipated 
operational needs. The first major project which 
was carried through to large-scale production 
was for the T-5 fuze to be used with the Army’s 
4^4-in. (M-8) rocket. The desired characteris- 
tics for this fuze 2 ’ 3 were, in addition to the 
general requirements stated above, (1) the 
complete fuze should fit into a cylindrical con- 
tainer approximately 2% in. in diameter and 


5 in. long, with an allowable conical extension 
on the front end of the cylinder about 2 in.; 

(2) at least 50 per cent of the fuzes were re- 
quired to function in the vicinity of an airplane 
target when fired on the rocket and within the 
lethal range of the fragments of the rocket; 

(3) the fuze was to be armed and operative 
approximately V 2 sec after firing; and (4) the 
fuze should have an SD element operating ap- 
proximately 9 sec after firing. 

The T-5 fuze project was limited in that the 
intended use was confined to a single missile 
and for a single application, antiaircraft. It 
was complicated by the fact that the design of 
the missile itself was not complete and its dy- 
namic fragmentation pattern was unknown. A 
dynamic fragmentation pattern was assumed 
from information supplied by the Services, but, 
as shown in Section 1.5, the assumptions were 
not strictly accurate. One very important com- 
promise was made in the requirements for the 
T-5 fuze from the ultimate Service needs. This 
was in respect to the temperature range 
throughout which the fuze could be used. Un- 
impaired operation between —40 and +160 F 
was desired, but because of the limitations of 
the dry batteries which were to be used to power 
the fuzes the low-temperature requirement was 
waived. Actually, the relaxing of this require- 
ment in the fuze did not impair the usefulness 
of the complete weapon since the rocket itself 
had low-temperature limitations not too dis- 
similar from those of the fuze. In order to 
reduce limitations due to possible deterioration 
of the battery power supply during shipment 
and storage, the design was made to allow final 
assembly of the fuze in the field using freshly 
tested batteries. 

Experience gained in the development and 
production of the T-5 fuze, combined with si- 
multaneous investigations for improved power 
supplies (Project SC-40), made possible much 
expanded, more rigorous, and more specific re- 
quirements for other radio proximity fuzes. 
These included fuzes for the following: (1) 
10,000-lb light-case [LC] bomb, (2) 4,000-lb 
LC bomb, (3) 2,000-lb general purpose [GP] 
bombs against both land- and water-borne tar- 
gets, (4) 2,000-lb glider and controllable bombs, 
(5) 1,000-lb GP bombs against water-borne 


SECRET 


OBJECTIVES AND MILITARY REQUIREMENTS 


3 


targets, (6) antiaircraft bombs for plane-to- 
plane bombing, (7) fragmentation and anti- 
materiel bombs of various sizes, and (8) large 
chemical bombs of 500-, 1,000-, and 2,000-lb 
sizes. 

The military requirements for these bombs 
were as follows: 4 * 5 

1. Adaptation to use in existing bombs, and 
to fit and drop in existing bomb racks. 

2. Strength enough to withstand handling 
and shipping and, unarmed, drop safely on nor- 
mal ground from 8,000 ft. 

3. No deterioration from storage at temper- 
atures from — 40 to +140 F. 

4. A minimum of adjustment and assembly 
in the field. 

5. A design which minimizes the possibility 
of triggering the fuze by enemy interference. 

6. Suitability for day or night use. 

7. Efficient operation at temperatures from 
—40 to +140 F. 

8. Efficient operation when released at any 
indicated airspeed above 150 mph. 

9. Efficient operation when released from al- 
titudes up to 35,000 ft. 

10. A minimum of 1,500 ft to arm. 

11. Consideration in design toward evolving 
a minimum number of fuze designs of suitable 
performance necessary to meet the require- 
ments of various sizes and types of bombs and 
targets. 

Burst heights were specified for only two of 
the foregoing applications, the T-40 and T-43 
fuzes for the 10,000- and 4,000-lb LC bombs. 3 
These heights were to be between 40 and 100 ft, 
with the mean preferably near 50 ft. This was 
believed to be the best height of operation for 
enhanced blast effect from these large high- 
charge bombs. The T-40 and T-43 were to be 
tail fuzes. The sensitivities or operating heights 
of the T-50 and T-51 fuzes intended for the 
other applications were not defined. It was, 
however, informally stated that, for antiper- 
sonnel and antimateriel use, burst heights of 
the order of 50 ft were desired. For the chem- 
ical bombs, burst heights of the order of 500 ft 
were believed best. Estimates in the former 
case were based on theoretical computations of 
fragmentation effect against shielded targets. 11 
The T-50 and T-51 fuzes were to be nose fuzes, 


interchangeable with the M-103 contact fuze. 

Following the development, production, and 
service testing of the T-50 bomb fuzes, minor 
changes, based on a fuller understanding of 
their operational properties, were made in the 
requirements for arming characteristics and 
for burst heights. These changes led to models 
T-89, T-90, T-91, and T-92, which are described 
fully in Chapters 4 and 5. 

Modifications were also requested in the T-50 
type fuze to allow its use on Navy rockets, 7 the 
modified fuzes carrying the designations T-30 
and T-2004 and differing from the T-50 mainly 
in arming characteristics. 

Experience gained in the development of the 
T-50 and T-51 fuzes made it evident that the 
physical size of radio proximity fuzes could be 
reduced sufficiently to allow their use on trench- 
mortar shells. Theoretical computations 14 indi- 
cated that a very appreciable gain in lethal 
effect could be obtained by air-bursting such 
shells. Accordingly, the Ordnance Department 
requested the development of the T-132, T-171, 
and T-172 fuzes 10 for use on the 81-mm mortar 
shells. According to military requirements, 
these fuzes must : 

1. Have a basic design also applicable to 105- 
mm and 155-mm mortar ammunition. 

2. Fit directly into the fuze cavity of stand- 
ard 81-mm mortar ammunition. 

3. Have sound ballistic design, minimizing 
any deleterious effect on projectile drag and 
stability as compared with fuzing with point 
detonating fuzes. 

4. When packaged, withstand rough han- 
dling, shipping, storage over extended periods, 
moisture, weather, and temperature cycles from 
-40 to + 140 F. 

5. When unpackaged, withstand loading op- 
erations, moisture, weather, and temperature 
cycles from —40 to +140 F for short periods, 
and withstand rough handling expected under 
service conditions incident to firing. 

6. Be provided with a cap or cover to pre- 
vent entry of mud or water into the air passage 
after removal of the fuzed round or fuze from 
its packaging, such can or cover to be removed 
upon withdrawal of safety pin or pins. 

7. Require a minimum of adjustment or 
assembly in the field. 


SECRET 



4 


INTRODUCTION 


8. Function at or near optimum mean effec- 
tive height on approach to ground over the 
range of angles of fall encountered with these 
projectiles. 

9. Limit combined early bursts and duds to 
15 per cent. 

10. Not be readily affected by enemy jam- 
ming or other interference. 

11. Have a secondary element capable of 
functioning on impact with minimum effect 
and independently of the primary element. 

12. Operate without detrimental interac- 
tion, due to mutual interference, when fired at 
random from weapons spaced closely together. 

13. Have an interrupted detonator-explosive 
train, safe against rough handling, dropping, 
or crushing, until properly armed by removal 
of safety pin or pins, acceleration of firing, and 
a fixed air travel. 

14. Have an arming delay mechanism which 
will insure detonator safety up to 400 yd (ten- 
tative estimated distance) from the mortar and 
which will also delay fuze activation until flight 
characteristics of the projectiles are sufficiently 
stable to minimize early burst due to poor sta- 
bility or action of the projectile and to permit 
efficient fuze operation at the target. 

15. Provide means for externally checking 
the safe position of the arming mechanism. 

16. Exhibit the above safety and operating 
characteristics under the following conditions: 
(1) temperature —40 to +160 F, (2) all 
weather conditions, and (3) night or day. 

The “mean effective height” referred to in 
requirement (8), although not specified, was 
understood to be of the order of 10 ft from 
theoretical computations, 14 but final specifica- 
tions would have to await effect field trials. 

It is to be noted that the requirements for 
T-132, etc., are much more detailed and rigor- 
ous than those for the T-5 fuze which had been 
laid down three years previously. In particu- 
lar, requirement (9) called for 85 per cent 
proper functioning of fuzes, whereas 50 per 
cent was allowed for the T-5. 

One apparently innocuous requirement intro- 
duced for security reasons applied to all bomb 
and rocket fuzes developed by Division 4. This 
was that all vacuum tubes used in the fuzes 
were to fail at accelerations between 10,000 


and 20,000<;. 33 The purpose of the requirement 
was to restrict the use of tubes suitable for 
shell fuzes to that application, thereby reducing 
the possibility that, through recovery of dud 
fuzes by the enemy, shell fuzes would be copied 
and used against our own air forces. As shown 
in Chapter 3, this requirement introduced some 
difficulties, because design considerations for 
microphonic stability and for ruggedness are I 
quite similar. Thus, in the course of developing 
suitable antimicrophonic tubes for use in the 
bomb and rocket fuzes, designs were developed 
which were rejected because the tubes would 
not fail at high accelerations. The requirement 
was withdrawn in the fall of 1944 (when shell 
fuzes were committed to battle under condi- 
tions where they might be recovered by the 
enemy) and thus did not apply to the mortar 
shell fuzes developed by Division 4. 


12 SELECTION OF THE DOPPLER-TYPE 
RADIO PROXIMITY FUZE 

The requirement that a fuze operate in the 
vicinity of target may be fulfilled by making 
the fuze sensitive to one of a variety of energy 
forms: radio, optic, acoustic, magnetic, etc. A 
comparison of the possibilities and limitations 
of various energy-sensitive devices is given in 
Volume 3, Chapter 2, of the Division 4 STR. 
Here we are concerned only with radio meth- 
ods. 

Among the radio types there are two general 
classes: active and passive. The active types 
generate and radiate energy and are sensitive 
to small amounts of energy after it is reflected 
from a target. Passive-type fuzes are merely 
sensitive to incident radio waves. In each of 
these general classes there are further divisions 
and subdivisions. 

Active-type fuzes may operate by depend- 
ence on interference between the original and 
the reflected waves, or operation may depend 
on the transit time for a pulse or train of waves 
to travel from the fuze to the target and back 
to the fuze again. Interference may occur in 
several ways. If there is relative motion be- 
tween the transmitter and the reflecting target, 
the reflected waves when received at the fuze 


SECRET 


OPERATION AND COMPONENTS OF DOPPLER-TYPE FUZES 


5 


will differ in frequency from the transmitted 
waves (doppler effect). Interference results in 
a beat note equal to the difference in frequency. 
On the other hand, if the transmitter is fre- 
quency or phase modulated, interference with 
the reflected waves produces a signal which is 
a function primarily of the distance to the tar- 
get. This principle is equivalent to that of the 
well-known FM radio altimeter. Pulsed or in- 
termittent circuits to determine time or dis- 
tance to target operate on essentially the same 
principles as the common forms of radar rang- 
ing devices. 

The simplest kind of passive proximity fuze 
requires the target to be a source of energy. 
Although this requirement can be satisfied for 
antiaircraft fuzes of the acoustic or infrared 
type, it would generally not hold for radio- 
sensitive devices. Consequently, a passive-type 
radio fuze would require auxiliary transmit- 
ting equipment as part of the fire control. 

In selecting an operating method for a radio 
proximity fuze, probably the most important 
consideration was simplicity. It was believed 
that if the fuze was too complicated, it would 
be impracticable on two grounds: (1) its vol- 
ume would be too large to satisfy ballistic re- 
quirements, and (2) it could not be manufac- 
tured in sufficient quantities in time to be of 
any value. Since fuzes are expendable devices, 
to be used only once, an appreciably different 
attitude toward production was required for 
radio proximity fuzes than for other types of 
radio equipment. Furthermore, a radio fuze is 
a device on which no adjustment is possible 
during its operation, hence reliability was a 
requirement which could not be compromised 
by the manufacturing problem. Thus, it ap- 
peared imperative to keep the design of a radio 
proximity fuze as simple as possible but still 
fulfill the military requirements. 

The simplest type of radio fuze is probably 
the passive type, but, since auxiliary fire con- 
trol equipment would be needed for its use, it 
does not meet the general requirement for “a 
minimum of special equipment and training” 
for its operational use. Passive-type radio 
fuzes were, however, seriously considered and 
investigated until it was definitely established 
that the transmitters required in active-type 


fuzes could be built in large quantities and made 
to operate reliably during the flight of the 
missile. 

Probably the simplest active-type radio fuze 
is the doppler type, since the transmitter in 
such a fuze requires no internal modulation or 
control circuits other than an audio-frequency 
amplifier. Furthermore, as is shown in detail 
in Chapters 2 and 3, there are sufficient design 
parameters available in doppler fuzes to adjust 
the position of operation along the trajectory 
of the missile approximately as desired. 

All radio proximity fuzes developed by Divi- 
sion 4 to the stage of adaptability to large-scale 
production are based on the doppler principle. 
Chosen initially because of its simplicity, the 
basic method has proved adequate to meet the 
major military requirements. More complicated 
systems have been surveyed and tested briefly, 
but none of these appeared simple enough to 
reduce to a mass-production design in time to 
be of value. 


13 OPERATION AND PRINCIPAL 

COMPONENTS OF DOPPLER-TYPE FUZES 

The actuating signal in a doppler-type fuze 
is produced by the interference with the trans- 
mitter in the fuze of the reflected energy from 
a target moving with respect to the fuze. The 
frequency of the reflected energy differs from 
the original by an amount (2v cos a)/X, where v 
is the velocity of the fuze in a coordinate system 
where the reflector is at rest, \ is the wave- 
length of waves radiated by the fuze, and a is 
the angle the velocity vector makes with the 
line between the missile and target. The inter- 
ference or combination of the two frequencies 
produces a low-frequency signal equal to 
(2v cos a) /l, which can be used to trigger an 
electronic switch. Selective amplification of the 
low-frequency signal is generally necessary. 

It is shown in detail in Chapter 2 that the 
concept of interference of the original and re- 
flected waves is analytically equivalent to a load 
variation on the transmitting oscillator. Hence, 
an r-f circuit which responds to variations in 
its loading will generate a target signal of fre- 
quency ( 2v cos a) /l. This signal may be de- 


SECRET 


6 


INTRODUCTION 


tected in a separate mixing circuit, oscillator 
diode [OD], or by a change in some parameter 
of the oscillator circuit, such as grid voltage, 
reaction grid detector [RGD] , or plate current, 
power oscillating detector [POD]. Tl;e designa- 
tions OD, RGD, and POD are further clarified 
in Section 3.1. 

The principal elements of a radio proximity 
fuze are shown in block diagram form in Fig- 
ure 1. The dashed lines between the oscillator 
and detector indicate that the two functions 
may be combined. 


ANTE NNA 



POWER SUPPLY ARMING 

Figure 1. Block diagram showing principal 
components of radio proximity fuze, doppler 
type. 

Operation of the fuze occurs when the output 
signal from the amplifier reaches the required 
amplitude to fire the thyratron. For a given 
orientation of the fuze and target, the ampli- 
tude of the target signal produced in the oscil- 
lator-detector circuit is a function of the dis- 
tance between the target and the fuze. Hence, 
by proper settings for the gain of the amplifier 
and the holding bias on the thyratron, the dis- 
tance of operation may be controlled. Distance, 
however, is not the only factor which requires 
consideration. Orientation or aspect is very im- 
portant, particularly against aircraft targets, 
since operation should occur at that point on 
the trajectory when the greatest number of 
fragments will be directed toward the target. 

For most missiles, the greatest number of 
fragments are directed upon detonation ap- 


proximately at right angles to the axis of the 
missile. The dynamic fragmentation pattern 
for an M-8 rocket is shown in Figure 2, b and its 
essential features pertaining to fuze design are 
typical of most missiles except that for higher- 
velocity projectiles, the side lobes are inclined 
forward toward the line of flight. The graph 
shows the density of the fragments per unit 
area of a sphere drawn about the missile as 
a function of the angle between the direction 
of the fragments and the axis of the missile. 
The angle 0 m represents the latitude angle along 
which the greatest number of fragments are 
directed. The three-dimensional pattern would 
be that obtained by rotating the curve in Fig- 
ure 2A about the flight axis. The static frag- 
mentation pattern of a 500-lb GP bomb is 
shown in Figure 2B. The dynamic pattern, 
obtained by the vectorial addition of velocities 
due to the bomb’s motion and due to the explo- 
sion, would be tipped forward a few degrees. 

For trajectories which would normally pass 
by the target without intersecting it, there will 
be optimum chance of damage if detonation of 
the missile occurs when the target makes an 
angle 0 m with the missile. However, for trajec- 
tories which would intersect the target, the 
missile should come as close to the target as 
possible before detonation. Hence, the basic re- 
quirements for directional sensitivity of a 
proximity fuze for antiaircraft use are (1) the 
sensitivity should be a maximum in the direc- 
tion corresponding to maximum lateral frag- 
mentation density of the missile, and (2) the 
sensitivity should be a minimum along the axis 
of the missile. Directional sensitivity of this 
type can be obtained by using the missile as an 


b It was erroneously assumed during the development 
of the T-5 fuze and in the absence of experimental data 
that the latitude (dynamic case) of maximum fragment 
density for the M-8 rocket would lie between 60 and 70 
degrees. Actually the density of lethal fragments in 
this direction is greater than shown in Figure 2A be- 
cause the contribution of the relatively low-velocity 
fragments from the rocket body are not shown in the 
figure. For high-velocity missiles, such as antiaircraft 
shells, the component of velocity due to the shell’s for- 
ward motion gives a very appreciable forward tilt to 
the dynamic fragmentation pattern. Also, in the case 
of higher-velocity aircraft rockets [HVAR] such as the 
5-in. HVAR, the latitude of maximum fragmentation 
density is about 66 degrees. Fuzes for this rocket (T-30) 
were developed later in World War II. 




SECRET 


OPERATION AND COMPONENTS OF DOPPLER-TYPE FUZES 


7 


antenna with the axis of the missile corre- 
sponding to the axis of the antenna. With the 
fuze in the forward end of the missile, such an- 
tennas are end-fed by means of a small elec- 
trode or cap on the nose of the fuze. Additional 
control over the sensitivity pattern of the fuze 
is possible by means of the amplifier gain char- 
acteristic. As pointed out previously, the fre- 


For use against surface targets, proximity 
fuzes are designed for an optimum height of 
burst, depending on the nature of the target 
and the properties of the missile. When frag- 
mentation bombs are air burst, the possible 
damage to shielded targets is substantially in- 
creased. Figure 3 shows a cross-sectional view 
of a typical shielded target: a man in a fox- 



Figure 2. Fragmentation patterns of missiles. 

The amplitude represents the relative density of the fragment as a function of the latitude angle around the axis of the missile. 
Figure 2A is for the M-8, 4.5-in. rocket and shows the dynamic pattern; i.e., directional allowance has been made for the effect 
of the velocity of the rocket. The graph, which is based on data in reference 19, does not include the contributions of fragments 
from the rocket motor. The latter are large, slow-moving, relatively few in number, and add to the pattern shown in the region 
between 45° and 90°. Figure 2B is a static pattern for the M-43, 500-lb GP bomb and is based on data in reference 11. The effect 
of bomb velocity on fragment direction is very slight (due to the relatively low velocity of the bomb) and would shift the maximum 
of the pattern forward of the order of 5°. 


quency of the target signal is {2v cos a) /l. The 
angle a varies rapidly as the missile passes the 
target, and if maximum gain occurs when 
a = 6 m there will be greater likelihood that the 
missile will be detonated at the proper point on 
its trajectory. More detailed discussion of these 
features is given in Sections 2.8 and 2.11 and 
in Sections 3.2 and 3.5. 


hole. The man is shielded from fragments from 
any bomb detonating either side of the hole and 
below the dashed lines. The angles <f> R and <f> L , 
which the lines make with the horizontal, are 
called the shielding angles for the respective 
directions. It is thus seen that, as the <j> s 
increase, higher burst heights will be neces- 
sary to expose the targets. An upper limit on 


SECRET 


8 


INTRODUCTION 


burst height is set by the lethal range of the 
bomb fragments since these fragments lose 
velocity rapidly as they travel from the point 
of explosion. Hence, the height of an air burst 
should be great enough to expose an appreci- 
able number of targets but not so high that the 
fragments will be impotent when they strike 
the targets. 

Most computations and evaluation tests for 
the optimum height of air burst for bombs 
have been on the basis of a 10° shielding or 
safety angle. c The optimum height varies only 



Figure 3. Sectional view of a soldier in fox- 
hole, typical shielded target. Soldier is protected 
from fragments from explosions below dashed 
lines. Angle these lines make with horizontal are 
called shielding, or safety, angles. 

slightly for the various striking angles and 
velocities with which bombs may approach the 
ground. Hence, it is desirable to design a fuze 
for ground-approach use which will give essen- 
tially constant burst heights for the various 
approach conditions. 

An approach to this requirement is to have 
maximum radio sensitivity along the axis of 
the bomb , with essentially constant sensitivity 

c See references 11, 12, and 13 for theoretical values 
and reference 16 for effect field tests. It should be 
pointed out that the size of the elementary target is a 
primary consideration in the computation of optimum 
burst heights. From this point of view, overhitting on 
targets of finite size is decreased as the burst height 
increases. Thus, an optimum burst height is determined 
by the lethal range of fragments on the one hand and a 
height where overhitting becomes excessive on the other. 


to about 45 degrees on either side of the axis. 
(For most release conditions used operation- 
ally, bombs strike the ground with an angle to 
the vertical of less than 45 degrees.) A short 
dipole antenna mounted transversely to the 
bomb’s axis and on the nose of the bomb essen- 
tially meets this requirement. In addition, it is 
necessary to design the amplifier of the fuze to 
give constant amplification for the range of 
doppler frequencies which might be encoun- 
tered because of various approach velocities. 

On the other hand, it was found that fairly 
good ground-approach performance could be 
obtained with fuzes with axial antennas by de- 
signing the amplifiers to compensate for the 
appreciable decrease in radiation sensitivity in 
the forward direction. For example, steep 
angles of approach in general mean high ap- 
proach velocities with higher doppler frequen- 
cies. Thus, a loss in radiation sensitivity with 
steep approach can be compensated by an in- 
crease in amplifier gain for the higher doppler 
frequency. Details of such design are given in 
Section 2.2. 

A miniature triode is used for the oscillator 
in the fuze and a pentode for the amplifier. 
When a separate detector is used, a tiny diode 
provides the required rectification. A miniature 
thyratron serves as the triggering agent and 
a specially developed electric detonator initiates 
the explosive action. Details concerning the de- 
sign of these elements are presented in the vari- 
ous sections of Chapter 3. 

Energy for powering the electronic circuits 
is obtained in the later fuze models from a 
small electric generator. This is driven by a 
windmill in the airstream of the missile. A rec- 
tifier network and voltage regulator are essen- 
tial parts of the power supply. Design details 
of the generator power supply, as well as 
earlier battery power supplies, are given in 
Section 3.4. 

The arming and safety features of the radio 
proximity fuzes are closely tied in with the 
power supply. This is a natural procedure since 
an electronic device is inoperative until electric 
energy is supplied. Arming a radio proximity 
fuze (generator type) consists of the following 
operations: (1) either (a) removal of an arm- 
ing wire which frees the windmill, allowing it 


PRODUCTION OF PROXIMITY FUZES 


9 


to turn in the airstream (bomb fuzes) or (b) 
actuation of a setback device freeing the drive 
shaft of the generator and allowing it to turn 
(rocket and mortar-shell fuzes), (2) operation 
of the generator to supply energy to the fuze 
circuits, (3) connection of the electric detona- 
tor into the circuit after a predetermined num- 
ber of turns of the vane corresponding to a 
certain air travel, and (4) removing a mechani- 
cal barrier between the detonator and booster 
prior to which explosion of the detonator would 
not explode the booster. Generally, operations 
(3) and (4) occur simultaneously by motion 
of the same device. 

Additional safety is provided by the fact that 
unless the generator of the fuze is turning rap- 
idly the fuze is completely inoperative. A mini- 
mum airspeed of approximately 100 mph is 
required to start the generator turning. Details 
of the arming system are given in Chapter 4. 


14 PRODUCTION OF PROXIMITY FUZES 

The course of the development of radio prox- 
imity fuzes for fin-stabilized missiles and the 
actual nature of the devices placed in produc- 
tion for Service use were influenced by many 
factors other than fundamental technical con- 
siderations. Time and expediency had a major 
influence on all designs. In order to have fuzes 
available for use as soon as possible, tooling for 
large production was frequently started before 
development was complete. This meant that 
when further development indicated certain de- 
sign changes to be imperative or desirable the 
extent of the changes which were made was 
controlled by the degree of the changes required 
in tooling or by the amount of time which 
would be lost by making the changes. Further- 
more, no components could be included in the 
design which would take too long to acquire in 
the necessary quantity nor could production 
techniques be considered which were over- 
elaborate and time consuming. 

Specific Service requirements varied as the 
course of World War II changed, and, because 
of the pressing demand for speed, fuze designs 
for the new requirements made much more use 


of the tools and techniques employed in preced- 
ing models than if production had started out 
fresh. For example, the greatest urgency early 
in World War II was for antiaircraft weapons, 
and stress was placed on fuzes for both bombs 
and rockets for this purpose. When the Allies 
acquired undisputed air superiority, the major 
proximity fuze requirements were shifted to 
the ground-approach operation. Thus, the T-50 
type bomb fuze, which employs the axial radio 
antenna, ideal for antiaircraft use and initially 
designed for that purpose, was adapted to 
ground-approach use. The T-51 fuze, which em- 
ploys the transverse antenna specifically devel- 
oped for ground-approach use, was used much 
less extensively for this application because its 
initial lower priority made it available later in 
World War II. 

More detailed information relating to the 
sequential development of radio proximity 
fuzes is given in the history of Division 4. The 
subject is mentioned here only to emphasize 
that the technical phases of the development 
were not always controlled by straightforward 
engineering design considerations. 

After the operation of a fuze design was 
found satisfactory by laboratory and field tests, 
it was necessary to determine its practicability 
for mass production. Pilot construction lines 
were used for this purpose, and it was the 
policy of Division 4 to require the construction 
of about 10,000 pilot-line fuzes with suitable 
performance characteristics before releasing a 
design to the Armed Services. Usually the tools 
developed for the pilot-line work were used also 
for final production. Large-scale procurement 
was handled by the Services, but Division 4 
participated in many phases of it, largely in an 
advisory capacity. The various technical aspects 
involved in the production of radio proximity 
fuzes are presented in Chapter 6. 

The radio proximity fuzes developed by Divi- 
sion 4 to the stage of large-scale production are 
as follows. More detailed information concern- 
ing the characteristics of these fuzes is given in 
Chapter 5. 

M-8 Rocket Fuzes 

1. T-5, an antiaircraft battery-powered fuze 
for the 4.5-in. M-8 rocket. This fuze is shown in 


SECRET 



10 


INTRODUCTION 


Figure 4. Approximately 370,000 were pro- 
cured by the Army. 

2. T-6, a ground-approach fuze, for use as an 
artillery weapon on the 4.5-in. M-8 rocket. This 
fuze is a variation of the T-5, having a longer 



Figure 4. Radio proximity fuzes for rockets. 
These are from left to right: (1) T-5 fuze for 
4.5 in. M-8 rocket for air-to-air use (T-6 ground- 
to-ground fuze is identical in appearance to 
T-5) ; (2) T-2004 fuze for 5-in. AR rocket for 
air-to-ground use; and T-2005 multiple-purpose 
fuze. 

arming time, about 6 sec compared to 1.0 sec, 
and no SD element. It is identical in exterior 
appearance to the T-5. Approximately 300,000 
of the T-5 fuzes were converted after comple- 
tion to T-6 fuzes. 

3. T-12, a generator-powered fuze for use on 
the M-8 rocket. This fuze was not placed in 
large production primarily because of curtail- 
ment in requirements for the M-8 rocket. 

Bomb Fuzes 

1. T-50-E1, a generator-powered ground- 
approach fuze for use primarily on the 260-lb 
M-81 fragmentation bomb, the 100-lb M-30 GP 
bomb, and the 2,000-lb M-66 GP bomb. This 
fuze, which uses the bomb as a radio antenna, 
was planned for air-to-air use when develop- 
ment started but was changed to ground- 
approach application before development was 
completed. Its radio transmitter operates in the 
Brown frequency band. This fuze was set to 


arm after 3,600 ft of air travel. It is shown in 
Figure 5. 

2. T-50-E4 is similar to the T-50-E1 fuze ex- 
cept that its transmitter operates in a different 
frequency band (White band), giving optimum 
performance on the 500-lb M-64 and the 1,000- 
lb M-65 GP bombs. Approximately 130,000 
T-50-E4 and T-90 fuzes were procured by the 
Army. 

3. T-89, an improved T-50-E1 type fuze, giv- 
ing more uniform burst heights. It also differs 
from T-50-E1 in that arming setting can be 
checked more readily in the field. Approxi- 
mately 140,000 T-50-E1 and T-89 fuzes were 
procured by the Services. This fuze is similar 
in appearance to the T-91 fuze, shown in Fig- 
ure 5. 

4. T-91 (later designation, M-168), a varia- 
tion of the T-89, developed specifically to meet a 
naval requirement of higher burst heights than 
the T-89 for low-altitude bombing. This fuze 
is set to arm after 2,000 ft of air travel. Ap- 
proximately 120,000 T-91 fuzes were produced. 

5. T-92, a variation of the T-90 developed to 
meet the same performance requirement as the 



Figure 5. Radio proximity fuzes for bombs. 
These are, from left to right: (1) T-50-E1 fuze 
for air-to-ground use on M-30 and M-81 bombs; 

(2) T-91 fuze, a later and improved version of 
T-50-E1, for use on M-30, M-81 and M-64 bombs; 

(3) T-51 fuze, air-to-ground use, for use on all 
bombs of 100-lb size or larger; and (4) T-82 
fuze for use paralleling T-51. 

T-91 of higher burst heights in low-altitude 
bombing. It is similar in appearance to the T-91 
fuze. Approximately 70,000 were produced. 

6. T-51 (later designation, M-166), a gen- 
erator-powered bomb fuze with a transverse 
antenna for ground-approach use on all GP, 
fragmentation, and blast bombs of 100-lb size 


GENERAL EFFECTIVENESS OF PROXIMITY FUZES 


11 


or larger. Burst heights with the T-51 are gen- 
erally higher than with T-50 type fuzes. This 
fuze was set to arm after 3,600 ft of air travel. 
Approximately 350,000 were procured by the 
Services. 

7. T-82, a generator-powered bomb fuze 
with transverse antenna of somewhat different 
physical dimensions than the T-51. It was de- 
veloped for the same general purpose as the 
T-51, but, when success of the latter was as- 
sured, further development of the T-82 was 
turned over to the Army. 8 It had not reached 
the production stage at the time of the transfer. 

Later Rocket Fuzes 

1. T-30 (Navy designation, Mk-171), a gen- 
erator-powered rocket fuze for air-to-air use, 
particularly on the Navy’s HVAR and the 5-in. 
aircraft rocket [AR]. This fuze is physically 
very similar to the T-91 bomb fuze and only 
slightly different electrically. Its arming sys- 
tem is different in that the acceleration of the 
rocket is essential to its operation. This fuze 
had just reached a production rate of 10,000 
per month at the end of World War II. 

2. T-2004 (Navy designation, Mk-172), a 
generator-powered rocket fuze for ground- 
approach use. It is similar to the T-30, but is 
somewhat less sensitive and has a longer arm- 
ing time. Approximately 110,000 were pro- 
cured by the Services. A photograph is shown 
in Figure 4. 

3. T-2005, a miniature generator-powered 
rocket fuze for either antiaircraft or ground- 
approach use (by a change-over switch). It is 
similar electrically to the T-30 and T-2004. De- 
velopment of this fuze was initiated by Divi- 
sion 4 but turned over to the Army for further 
work before the point of large-scale production 
was reached. A photograph of the fuze is shown 
in Figure 4. 

Trench-Mortar Fuzes 

1. T-132, a generator-powered ground-ap- 
proach fuze for use on the 81-mm trench-mor- 
tar shell. This fuze, shown in Figure 6 along 
with the T-171 and T-172, uses the body of the 
shell as an antenna. It also incorporates a novel 
production technique, i.e., printed or stenciled 
electric circuits. Tools were being set up for a 


production rate of approximately 100,000 per 
month when World War II ended. 

2. T-171, a generator-powered ground-ap- 
proach mortar-shell fuze, similar to the T-132 



Figure 6. Radio proximity fuzes for trench 
mortar shells. These are, from left to right: 

(1) T-132 fuze using electric circuits “printed” 
on ceramic plates; (2) T-171 fuze, electrically 
similar to T-132 but with standard electrical re- 
sistor and condensers; and (3) T-172 fuze with 
loop antenna. 

except that it employs the more standard cir- 
cuit-assembly techniques. Tools were being set 
up for production rate of about 125,000 per 
month when World War II ended. 

3. T-172, a generator-powered ground-ap- 
proach mortar-shell fuze with a loop antenna. 
This antenna has essentially the same direc- 
tional properties as the transverse antenna of 
the T-51 bomb fuze. Tools were being set up for 
a production rate of about 250,000 per month. 

Development of the T-40 and T-43 bomb tail 
fuses (referred to in Section 1.2) for the 4,000- 
and 10,000-lb blast bombs was not completed 
because the T-51 nose fuze appeared to be ade- 
quate to meet all the requirements. As shown 
in Chapter 9, tests of the T-51 fuzes (with 
minor modifications) on M-56 (4,000-lb) bombs 
gave excellent performance. No 10,000-lb 
bombs were made available for field tests. 

15 GENERAL EFFECTIVENESS OF 
PROXIMITY FUZES 

Although the final answer on the effective- 
ness of a new military weapon is supplied by 


SECRET 


12 


INTRODUCTION 


its performance in battle, the best quantitative 
measure of relative effectiveness under con- 
trolled conditions can be obtained from care- 
fully planned field trials. A number of evalua- 
tion tests have been carried out on radio 
proximity fuzes. These can be grouped into the 
following categories. 

1. Evaluation of conformance to require- 
ments. 

2. Evaluation as a weapon: 

a. Antiaircraft use (fragmentation ef- 
fect) . 

b. Air burst (ground approach on frag- 
mentation bombs and rockets). 

c. Air burst on blast bombs. 

d. Air burst on chemical bombs. 

e. Air burst on fire bombs. 

Most of the tests conducted by Division 4 
other than strictly developmental tests were in 
the first category above. The Services also car- 
ried out extensive tests in the first category but 
generally after the fuzes were in production. 

Tests and evaluation studies in category 2 
above were usually carried out by the Services 
or by other NDRC divisions and therefore are 
not properly within the scope of this volume. 
The results, however, are of interest in giving 
a more complete picture of the evaluation of 
radio proximity fuzes and accordingly will be 
referred to briefly. Such evaluations, of course, 
depend primarily on the properties of the mis- 
sile which carry the fuzes and in no cases were 
the missiles designed for proximity operation. 
Now that proximity fuzes have been established 
as practicable devices, certain missiles, such as 
fragmentation bombs for air-burst use should 
be redesigned to increase greatly their effec- 
tiveness as weapons. 

Typical missiles equipped with proximity 
fuzes are shown in Figure 7. 

Evaluation of Conformance to 
Requirements 

Detailed evaluations of the conformance of 
the fuzes to the military requirements are pre- 
sented in Chapters 5 and 9. In this section, a 
brief abstract is given of the most important 
results for production fuzes. Generally, the re- 


liability of the radio proximity fuzes for bombs 
and rockets was about 85 per cent, that is, 85 
per cent of the fuzes would be expected to func- 
tion on the target as required. Of the remainder 
about 10 per cent could be expected to function 
before reaching the target (random bursts) 
and 5 per cent not to function at all. The 10 per 
cent or so random functions were distributed 
along the trajectory between the end of the 
arming period and the target. In many thou- 
sands of tests, no fuze functions were observed 
before the end of the arming period. 



Figure 7. Radio proximity fuzes on typical 
missiles. These are, from bottom to top: (1) 
T-132 fuze on 81-mm M-56 mortar shell; (2) 
T-91 fuze on M-81-A 260-lf fragbentation bomb; 

(3) T-51 fuze on the M-64, 500-lb general pur- 
pose bomb; and (4) T-2004 fuze on 5-in. HVAR 
rocket. 

General reliability and proximity sensitivity 
(function heights) for the various production 
models follow. 

1. T-5 Fuze. Acceptance tests on over 4,000 
T-5 fuzes against a mock airplane target 
showed the following results: 

a. 81 per cent proper functions in the 
vicinity of the target. 

b. 2 per cent functions just beyond the 
target. 

c. 13 per cent early functions between 
arming and the target. 

d. 4 per cent duds. 

The time of flight in normal acceptance tests 
(see Chapter 8) was inadequate to allow test- 


GENERAL EFFECTIVENESS OF PROXIMITY FUZES 


13 


in g of the SD feature. Separate tests on the SD 
showed it to be 96 per cent reliable at an aver- 
age time of 8.5 sec after firing. Ninety per cent 
of the SD functions were between 6.5 and 11 
sec. These figures refer to the mechanical SD 
(see Chapter 4) used in later models. An elec- 
tric SD used in earlier models (see Section 3.3) 
was less reliable. 

The vicinity of the target was defined as 
within a 60-ft impact parameter of an 0.8-scale 
target of a medium bomber. For more detailed 
discussion of a proper definition of “vicinity of 
the target” see Section I.5.2. 1921 

2. T-6 Fuze. The percentage of proper func- 
tions for the T-6 ground-approach fuze depends 
on the time of flight of the rocket, the number 
of random functions increasing with the longer 
trajectories. For maximum range, tests on over 
1,500 rounds indicated the following perform- 
ance. 

a. 80 per cent proper functions. 

b. 16 per cent random functions. 

c. 4 per cent duds. 

Proper functions were defined as operation 
between 6 and 100 ft above ground. 

3. T-50-E1 and T-89 Fuzes. Acceptance tests 
on 100 lots (lots averaged about 1,000 fuzes 
and field tests were made on about 18 fuzes 
from each lot) of T-50-E1 and T-89 bomb fuzes 
showed 

a. 83 per cent proper functions. 

b. 13 per cent random functions. 

c. 4 per cent duds. 

Proper functions for ring-type bomb fuzes 
(axial antennas) were defined as between 6 and 
100 ft over a water target. The average burst 
height was 33 ft. 

4. T-91 Fuzes. The first lots of T-91 bomb 
fuzes were about the same quality as the T-50- 
E1 fuzes. However, later lots (T-91-E1 using 
the RGD circuit, see Section 3.1) showed the 
following average for 27 lots. 

a. 92 per cent proper functions. 

b. 7 per cent random functions. 

c. 1 per cent duds. 

The average height of function was 60 ft over 
a water target. 

5. T-50-E4 and T-90 Fuzes. Tests on 130 lots 
of T-50-E4 and T-90 bombs showed 

a. 78 per cent proper functions. 


b. 19 per cent random functions. 

c. 3 per cent duds. 

The average height of function was 40 ft. 

6. T-92 Fuzes. Tests on 50 lots of T-92 bomb 
fuzes showed 

a. 58 per cent proper functions. 

b. 34 per cent random functions. 

c. 8 per cent duds. 

The average height of function was 34 ft. 

The inferior performance of T-92 fuzes was 
due to unusual dependence of the fuze on the 
electric properties of the test missile, the M-64 
bomb. It was found that, on bombs which had 
been carefully prepared to reduce variable con- 
tact between the fin and the bomb body, scores 
equal to those with other fuzes were obtained. 
When it was definitely established that the poor 
performance of the T-92 was due to this cause 
and consequently could not be improved by 
more rigorous production control, further pro- 
curement was terminated. It had meanwhile 
been shown that the T-51 and T-91 fuzes, which 
had become available, would fulfill the applica- 
tions for which the T-92 was intended. 

7. T-51 Fuzes (M-166). Field tests on 230 
lots of T-51 bomb fuzes showed 

a. 91 per cent proper functions. 

b. 9 per cent random functions. 

c. 1 per cent duds. 

The average height of function over the water 
target was 110 ft. The proper function range 
included heights up to 200 ft for bar-type fuzes. 

8. T-2004 Fuzes. Field tests on 75 lots of 
T-2004 rocket fuzes showed 

a. 94 per cent proper functions. 

b. 3 per cent random functions. 

c. 3 per cent duds. 

The average height of the proper functions was 
30 ft. 


1,5,2 Evaluation as a Weapon 

Antiaircraft Use 

A careful analysis of the T-5 fuze on the M-8 
rocket as an antiaircraft weapon was made by 
the Applied Mathematics Panel [AMP]. 19 ' 21 
The study was based on the experimental per- 
formance of the fuze against a mock aircraft 
target, fragmentation data of the rocket, dis- 




14 


INTRODUCTION 


persion data on the rocket when fired from an 
airplane, and vulnerability of a twin-engine 
enemy aircraft, in particular the JU-88, to 
fragmentation damage. 

Conclusions of these studies were as follows : 

1. When fired from 1,000 yd directly astern 
with a standard deviation in firing error of 
about 50 ft (17 mils), a single round has one 
chance in * 10 of preventing a twin-engined 
bomber from returning to base provided it 
cannot return to base on one engine. 

2. If return to base on one engine is pos- 
sible, there is one chance in 16 that a single 
round will prevent its return. 

3. If a delay of about 50 ft were incorporated 
in the fuze, to bring the vulnerable part of the 
target in a region of greater fragmentation 
density, the above probabilities would be in- 
creased to 1 in 4 and 1 in 6. 

The greater effectiveness of the weapon with 
the delay was due to the fact (as shown in Fig- 
ure 2) that the latitude of greatest fragmenta- 
tion density of the rocket was approximately at 
right angles to the axis of the rocket, whereas 
the fuze, as shown in Chapters 2 and 3, had 
been designed from an assumed latitude of 
maximum density of about 70 degrees. A delay 
of the amount recommended in the AMP report 
would have brought the target in the region of 
maximum fragment density. Such a delay could 
have been incorporated readily in the fuze had 
the tactical demand for this weapon in 1944 
been as high as it was in 1942. However, there 
appeared to be little likelihood that M-8 rockets 
would be used as air-to-air weapons, so the 
fuzes were not modified. 

The probability of obtaining a crippling di- 
rect hit by an M-8 fired under the same condi- 
tions is about 1 in 100. 

Limited tests and evaluations were made of 
the 5-in. AR and HVAR equipped with T-30 
fuzes as antiaircraft weapons. At the Naval 
Ordnance Test Station at Inyokern, California, 
some 70 rounds were fired from a fighter air- 
plane at a radio-controlled plane in flight. 18 At 
about 400-yd range, over 55 per cent of the 
rounds functioned on the target. Eight high- 
explosive [HE] loaded rounds were fired, four 
of which functioned on the target, and three of 
the four destroyed the targets. Presumably, 


most of the rounds which did not function on 
the target were beyond the range of action of 
the fuzes. 

The Applied Mathematics Panel made an in- 
formal study of the effectiveness of AR and 
HVAR equipped with proximity fuzes. 22 For 
these rockets it was found, presumably because 
of their higher velocities, that the optimum 
burst surfaces were inclined forward from the 
equatorial plane of the rocket and not at right 
angles to it, as was the case for the M-8 rocket. 
No experimentally determined burst surface 
patterns were obtained for T-30 fuzes but, 
assuming the same burst pattern as for T-5 
fuzes, the effectiveness was nearly optimum. 
For example, the probability of destroying an 
aircraft with an HVAR with a firing error of 
25 mils at 1,000-yd range was 0.4, and with 15 
ft optimum delay was 0.63. Further details are 
in the AMP report. 

Air Burst for Ground Targets 

The Army Air Forces [AAF] carried out ex- 
tensive evaluations of the effectiveness of air- 
burst bombs against shielded targets using 
T-50 and T-51 fuzes on M-81 (260-lb fragmen- 
tation) and M-64 (500-lb GP) bombs. Bombs 
were dropped on a large effect field covered 
with target boards 2x6 in. in trenches 1 ft deep. 
For equivalent airplane loads of properly func- 
tioning bombs dropped on 12-in. deep trench 
targets, conclusions from the AAF report 
are : 16 

1. Air-burst 260-lb M-81 fragmentation 

bombs and 500-lb M-64 GP bombs produce 
about 10 times as many casualties as contact- 
burst 20-lb M-41 fragmentation bombs when 
trenches are 15 ft apart. (A casualty is defined 
as one or more hits per square foot, capable of 
perforating % in. of plywood.) 

2. Optimum height of burst for maximurfi 
casualty effectiveness is between 20 and 50 ft, 
with only slight variation through this range. 

The British carried out similar appraisals, 
using T-50 fuzes on M-64 bombs. 26 There are 
several differences in details of the tests, par- 
ticularly in the matter of evaluating the effec- 
tiveness of surface-burst bombs. The British 
Ordnance Board made an appreciable allow- 
ance for the blast effect of both the contact- 


GENERAL EFFECTIVENESS OF PROXIMITY FUZES 


15 


fuzed bombs and variable-time [VT] fuzed 
bombs and arrived at a superiority factor of 
4 to 1 for the latter against shielded or en- 
trenched targets. 

The AAF also evaluated the M-8 as an air- 
to-ground weapon with both VT (T-5) and 
contact fuzing. 17 The summary report con- 
cluded that the weapon was relatively ineffec- 
tive against shielded surface targets, although 
the casualties per round with VT fuzing were 
about five times as high as with contact fuzing. 

Air Burst for Blast Bombs 

Studies by Division 2, NDRC, 23 and by the 
British 25 demonstrated that when large blast 
bombs are air burst at about 50 to 100 ft above 
ground, the area of demolition could be in- 
creased from 50 to 100 per cent. No full-scale 
tests were carried out to verify these conclu- 
sions, but it was established that the T-51 fuze 
could be used on both the 4,000-lb (M-56) 
American bomb (Chapter 9) and the 4,000-lb 
British bomb 27 to give air bursts at the proper 
altitudes. 

In cooperative tests by the Army, Division 4 
and Division 2, NDRC, 24 ’ 34 it was shown that 
air-burst bombs could be used in mine-field 
clearance. The advantages were primarily in 
increased reliability of clearance and absence 
of cratering. However, the use of air-burst 
bombs for this purpose does not markedly re- 
duce the number of bombs required to clear an 
area. 

Air Burst for Chemical Bombs 

A number of evaluations were made to deter- 
mine the effectiveness of air bursts on chemical 
bombs. In a carefully planned effect field test 
using T-51 and T-82 fuzes on 500-lb LC bombs, 
the British showed the areas of contamination 
with a mustard-type gas were 4 to 5 times 
greater than when the bombs were used with 
contact fuzes. 30 The increase was due to a more 
uniform distribution of the vesicant and avoid- 
ance of loss of material in craters. 

The Chemical Warfare Service and the Brit- 
ish cooperated in an extensive series of tests at 
Panama in simulated jungle warfare. A T-51 
fuze with reduced sensitivity effectively pro- 
duced air bursts of chemical bombs below tree- 


top canopies with efficient distribution of chem- 
ical materials. 28 ’ 29 

Air Burst for Fire Bombs 

The Army Air Forces evaluated the effective- 
ness of T-51 fuzes on fire bombs and found that 
for high-altitude bombing the distribution of 
incendiary material was appreciably improved. 
In this application, the gain due to an air burst 
was due to the elimination of loss of material 
in craters. 31 

1 5,3 Operational Use of Proximity Fuzes 

Proximity fuzes for bombs and rockets saw 
very limited operational use, primarily because 
they were introduced into action very late in 
World War II. Some of the factors which im- 
peded their initial operational use are dis- 
cussed in the history of Division 4. Other fac- 
tors, as well as a full summary of their use in 
World War II, are given in a memorandum by 
a member of the VT Fuze Detachment of the 
Ordnance Department. 32 Some excerpts from 
the latter reference are given in Chapter 9. 

Altogether, approximately 20,000 fuzes, pri- 
marily bomb fuzes, were used in action by the 
Army and the Navy in the Pacific, and in the 
European and Mediterranean Theatres of Op- 
eration [ETO] and [MTO]. In the last few 
weeks of the war in the Pacific, approximately 
one-third of all bomb fuzes used by carrier- 
based aircraft were proximity fuzes. The main 
targets were antiaircraft gun emplacements 
and airfields. 

No thoroughgoing analysis of the effective- 
ness of the fuzes operationally was possible, 
although the general reaction was very favor- 
able. Since the fuzes were used in all theaters 
so late in World War II, the major uses were 
of a trial or introductory nature. In all cases, 
these trial uses were followed by urgent re- 
quests for more fuzes, which usually, and par- 
ticularly in ETO and MTO, did not arrive until 
after World War II was over. All initial uses 
were in 1945, in February in the Pacific and in 
March in ETO and MTO. Reports concerning 
the effectiveness of the fuzes against gun em- 
placement targets generally stated that anti- 
aircraft fire was either stopped or greatly re- 


SECRET 



16 


INTRODUCTION 


duced after the air-burst bombs exploded. 

Although relatively little or no quantitative 
data as to the effectiveness of the fuzes was 
secured, their use was extensive enough to es- 
tablish their practicability as service items of 
ordnance equipment. Relatively little difficulty 
was experienced in the handling and use of the 
fuzes and none of these was serious or insur- 
mountable. Hence, with the effectiveness of 
proximity fuzes well established by effect field 


studies and operational practicability estab- 
lished by combat use, proximity fuzes appear 
assured of a permanent and increasingly im- 
portant position in modern ordnance. The tech- 
nical information presented in the succeeding 
chapters of this volume not only serves to pro- 
vide a full understanding of the properties of 
the fuzes which were developed and produced, 
but it also provides a firm and logical basis for 
future development. 


SECRET 


Chapter 2 

THE RADIATION INTERACTION SYSTEM 


21 INTRODUCTION 

rj 1 he PRECEDING chapter has explained what 
1 _ a proximity fuze is and has shown what the 
fuze must do by stating the military character- 
istics required for such a device. The basis 
upon which the radio reflection principle was 
selected as most suitable for a proximity fuze 
has been discussed, and some of the reasons for 
using the doppler principle have been pre- 
sented. We are now in a position to explain the 
working principles of the device and its engi- 
neering design. 

In discussing the working principles we are 
concerned with two essentially independent 
sets of phenomena: (1) those external to the 
fuze mechanism, i.e., the emission and recep- 
tion of radiation and its interaction with the 
target; and (2) those within the fuze itself, 
i.e., internal circuit behavior. 

The present chapter deals with the first 
group, external phenomena, which we call the 
radiation interaction system. To facilitate dis- 
cussion, an arbitrary dividing line is drawn at 
the point where the internal fuze circuit is 
electrically connected to the fuze antenna. As 
will be seen, it is possible to describe the ex- 
ternal phenomena so that their effect can be 
expressed as an appropriate variation of im- 
pedance at these antenna terminals. When the 
relation between the radiation interaction with 
the target and the variation of antenna im- 
pedance has been determined, the problem be- 
comes one of constructing a practical circuit 
which will respond properly to the changes 
seen at its terminals. 

It should not be inferred from this division 
of phenomena, for the purposes of discussion, 
that antenna design and circuit design are en- 
tirely independent. Each must be designed with 
due regard to the other, and both designs are 
dictated by such practical considerations as 
physical limitations of components and tactical 
utility. In fact it will become evident as the dis- 
cussion proceeds that the working principles of 

a By R. D. Huntoon and P. R. Karr. 


the fuze are quite simple and that the real dif- 
ficulty in making a practical proximity fuze lies 
in reaching an adequate compromise between 
a host of closely interrelated factors. The co- 
ordination of these various factors is treated 
in Section 3.5. 

Many of the phenomena treated in this chap- 
ter are shown to be negligible or unimportant 
for the type of doppler fuzes of immediate in- 
terest. The phenomena may, however, have 
appreciable importance for fuzes of other types 
or for more extensive applications of the pres- 
ent fuzes. For these reasons, the basic theory 
has been treated in appreciable detail by de- 
veloping considerable material found in ad- 
vanced textbooks on radiation and circuit 
theory. This approach should enable new in- 
vestigators in the field of proximity fuzes to 
familiarize themselves with the fundamental 
principles involved with a minimum of re- 
course to the technical literature. 


22 SPECIFICATION OF PROBLEM IN 
TERMS OF ANTENNA IMPEDANCE 

The fuze detects the presence of an obstacle 
in its radiation field by means of returning 
radiation reflected by the obstacle. The physical 
situation is thus characterized by an outgoing 
wave with a frequency determined by the fuze 
transmitter and a returning wave of much 
smaller amplitude, whose frequency may be 
different as a result of relative motion of fuze 
and reflector. In all the discussion which fol- 
lows, it will be assumed that the reflecting ob- 
stacles are linear reflectors, by which we mean 
that the strength of the reflected field is propor- 
tional to the strength of the incident field. It is 
shown in this section that the returning wave 
differs in frequency from the outgoing wave by 
an amount which can be calculated by the appli- 
cation of the doppler principle, and that under 
certain conditions, which hold for present fuze 
designs, this combination of outgoing and re- 
flected wave is exactly equivalent to a change 


SECRET 


17 


18 


THE RADIATION INTERACTION SYSTEM 


in antenna impedance. The usefulness and limi- 
tations of this concept are discussed. f 

2-21 Reflected Wave or Doppler 
Frequency Concept 

Consider a radiating system R which radiates 
a carrier of frequency /. Its field in any direc- 
tion x will be of the form 

E = (i) 

Let the radiation be received in a system R' 

moving with a velocity v in the direction —x, 
i.e., toward the system R. In this moving system 
of reference the field will be of the form 

E' = A'e i2rf ' [t ' ~ (x ' /c )l. (2) 

The phase of the wave is relativistically invari- 
ant, so that 

7) ») 

Now V and x' are related to t and x by the 

Lorentz transformation. Applying this gives 

when it is remembered that v is —dx/dt. 

At the present time relative velocity of fuze 
and target never exceeds 5,000 fps so that v/c 
is of the order of 5 X 10 -6 . Equation (4) can be 
rewritten 

(5) 

r =f ( 1+ k + lcft) = f + i ( 1 + 
which is close enough to 

r = / + J (6) 

which is recognized to be the normal doppler 
frequency shift. Thus the frequency received at 
the target is given by equation (6) above. The 
target reradiates, reflects, on this frequency, 
and a second application of the above argument 
leads to 

f" = / + p (7) 

where /" is the frequency of the reflected wave 
as seen at the fuze. For current fuze designs, 
the doppler or difference frequency 2v/l is of 


the order of a few hundred cycles per second 
out of a carrier frequency of the order of 100 
me and the error introduced by neglecting rela- 
tivistic effects is of the order of 10 -4 c. 

2 2 2 Reflection Equivalent to Change of 
Antenna Impedance 

The two-wave picture outlined above can be 
converted to the equivalent impedance picture 
quite simply. First, assume the system R' to be 
at rest, so that f — f' =/". Then the field of the 
system R, equation (1), can be written as 

E = KIe j2v[ft - - ( 8 ) 

where the dependence of E upon I, the antenna 
current, is shown explicitly. This field is re- 
flected from the target at distance x with a loss 
in amplitude and a phase shift 5 and returns as 
reflected field E r , given by 

E r = BKIeW* ~ (2 * /x) + 5] . ( 9 ) 

The constant B represents the loss at reflection 
and represents also the initial assumption that 
reflected field is proportional to incident field. 
The fuze antenna receives this reflected field E, 
and converts it to a voltage V r so that 

V r = B'KIe j2v [ft ~ + «, (10) 

showing that V r is proportional to /, the trans- 
mitting antenna current. The term B' replaces 
B and now involves an additional factor trans- 
lating field to voltage. 

At this point it is necessary to call attention 
to the fact that the radio fuzes herein described 
and to which the theory we are discussing is 
applicable use a common antenna for transmis- 
sion and reception and use the same terminals 
for transmission and reception. Thus the cur- 
rent I in equation (10) represents the trans- 
mitter current into the antenna terminals, and 
V r represents the voltage across those same 
terminals arising as a result of the presence 
of the reflector in space. Since ( V r /I ) is dimen- 
sionally an impedance, we may write 

V r = IZ r e j2 * ft , (11) 

where 

Z r = B'Ke j2 * [( -2*/A) + 6 )' ' (12) 

The constants B'K represent the magnitude of 
the reflected impedance Z r , and the term e j2 ^~ 2x/ ^ 


SPECIFICATION OF PROBLEM IN TERMS OF ANTENNA IMPEDANCE 


19 


shows the variation of the phase angle as the 
distance x to the target changes. In the above 
discussion, I has been assumed to be constant 
in the presence of the reflector. This assump- 
tion is made only for purposes of computing Z r ; 
the results obtained hold when I varies, as it 
normally does. 

Suppose now that the target moves toward 
the fuze with a velocity V — dx/dt. Then the 
rate of change of total phase 4> of the imped- 
ance is 



The frequency F with which the impedance Z r 
completes its phase cycle is given by 


F 


1 d<I> _ 2v 
2 nit ~ + \’ 


(14) 


a value identical with the doppler frequency 
derived above, equation (7). We thus see that 
the reflector can be replaced in the fuze antenna 
circuit by a reflected impedance Z r , whose am- 
plitude represents the strength of the reflected 
voltage and whose rate of change of phase cor- 
responds to the doppler frequency shift. In this 
derivation of the frequency F, we have neg- 
lected relativistic effects; these are, of course, 
negligible, just as in the preceding derivation. 

For fuzes having a common antenna for 
transmission and reception, using common ter- 
minals for both, we can represent the behavior 



Figure 1 . Vector representation of antenna 
impedance in presence of reflector. 


associated with a moving reflector in the radi- 
ation field by the vector diagram shown in 
Figure 1. 

In this figure Zn represents the impedance 


at the antenna terminals in the absence of all 
reflectors (free space). Its resistive and reac- 
tive components are Ru and X 1± respectively. 
The term Z r represents the reflected impedance 
and Zi the total antenna impedance with the 
reflector present. When a target moves toward 
the fuze with a velocity v, the end of Z r traces 
out a spirallike figure with an angular velocity 


= 2tF = 


47i -v. 


The radius increases as Z r increases. 


2 ' 2 ' 3 Approximations Involved in 
Impedance Representation 

Suppose we consider two systems, each en- 
closed in a box with only two terminals avail- 
able to the experimenter and no indications 
outside to show the contents of the box. Let 
box 1 contain a fuze antenna, space for radia- 
tion, and a moving reflecting target. Let box 2, 
identical in every external detail with box 1, 
contain within it a fixed impedance Z X1 and a 
variable impedance Z r with magnitudes selected 
according to the definitions above. 

In a steady-state condition, i.e., with go = 0 
and with the fuze in operation long enough for 
all transients to die out, no set of measure- 
ments can distinguish a difference between the 
contents of the two boxes, and they are for all 
purposes identical. 

If we test the two arrangements by suddenly 
applying the r-f voltage to the terminals, there 
will be a difference in the way in which the 
steady state is reached. This difference is 
analogous to the difference in the transient be- 
havior of two circuits A and B, where B is 
identical with A except for a length of perfect 
transmission line attached to its input termi- 
nals. If a signal were suddenly applied to the 
input terminals of A, a certain transient re- 
sponse would be obtained at the output of A. 
If the same signal were suddenly applied to the 
input of the transmission line attached to B, 
the transient response at the output of B would 
differ from that at the output of A because of 
the delays due to the transmission line. The 
steady-state behavior of the two circuits, how- 


SECRET 


20 


THE RADIATION INTERACTION SYSTEM 


ever, would be identical. Thus in the case of 
the fuze circuit we can apply the impedance 
concept, which is a steady-state concept, to 
those cases in which the delays associated with 
the radiation link are negligible. We now pro- 
ceed to show that these delays are unimportant 
in cases of interest. 

One effect of the finite transmission time of 
the waves is that at any time t the fuze receives 
a reflected signal which is characteristic of the 
target not at time t but at time (t —r/c), where 
r is the distance from target to fuze at the mo- 
ment when the signal which arrives at the fuze 
at time t started out from the target. This 
means that the fuze does not “know” its dis- 
tance from the target at any instant, but only 
what the distance was at a time (r/c) in the 
past. In the region of interest r/c is of the 
order of 10 -6 sec, during which time the fuze 
moves a distance of the order of 10 -3 ft. Thus 
this effect is seen to be of no importance in de- 
termining the position of function of the fuze. 
It may be pointed out, however, that for prox- 
imity fuzes which work on other principles, 
for example, the reflection of radiated sound, 
this effect may be of considerable importance. 

Another effect of the delay associated with 
the radiation link is that it introduces an effec- 
tive “time constant” in the fuze circuit because 
of the effect which the reflected voltage has on 
the antenna voltage, which in turn influences 
the reflected voltage, etc. A rough estimate of 
the order of magnitude of this time may be ob- 
tained by assuming the fuze and antenna sta- 
tionary and computing the time required for 
the fuze voltage to reach a steady-state value 
after being switched on. The time required to 
reach equilibrium is assumed for the purposes 
of this discussion to be associated entirely with 
the propagation of the waves in space and not 
at all with delay characteristics of the fuze cir- 
cuit itself. 

The presence of the reflector induces a volt- 
age in the fuze proportional to the voltage in- 
duced in the reflector by the fuze antenna. The 
above statement can be made more precise by 
including the time element; that is, suppose at 
time t = 0 , the fuze begins to radiate. Some of 
the radiation “bounces” back from the reflector, 
reaches the fuze again at time A t, usually ap- 


preciably less than 10 -6 sec, and induces a volt- 
age in the fuze antenna. This causes a change 
in the radiation; this changed radiation is re- 
flected by the target again, and its effect is felt 
back at the fuze at time 2 At. This process goes 
on until equilibrium is reached. 

For the sake of simplicity, assume that the 
distance of separation is such that the im- 
pressed and reflected voltage in the fuze an- 
tenna are always in phase. In this case the 
effect of the reflected radiation is to increase 
the voltage in the fuze antenna. Let k be the 
constant relating the voltage induced in the 
fuze antenna by reflected radiation to the volt- 
age in the fuze antenna, which was associated 
with the original radiation. For many cases of 
interest k is of the order of 0.01. Then the vari- 
ation in the fuze voltage starting from t — 0 
may be represented as in Figure 2, in which 
no attempt has been made to represent the true 
scale. In the figure F 0 represents the voltage at 
t — 0. The expression for this variation is 

F (t) = F 0 + kV(t- At), (15) 

which applies for t ^ At. For t < At, V ( t ) = F 0 . 
The equilibrium voltage V m is the limit of the 
series 

Foo = F 0 (1 + k -f~ k 2 -f- /c 3 -}- • • •), (16) 

- ,~E- < 17 > 

For k << 1, we have 

F ro « (1 + k) F 0 . (17a) 

Furthermore 

F (A0 = (1 + k) F 0 . (18) 

Thus we see that for small k the first reflection 
is responsible for most of the voltage change. 
This would be true for any other assumed 
phase relation between the impressed and re- 
flected voltages in the fuze. 

If desired, we may replace the stepwise vari- 
ation by a smooth curve, as shown roughly in 
Figure 2 ; this smooth curve may be represented 
analytically. To do this we replace V (t — At) in 
equation (15) by the quantity [V (t) — At 
( dV/dt )], the first two terms of the Taylor 
expansion. 


SPECIFICATION OF PROBLEM IN TERMS OF ANTENNA IMPEDANCE 


21 


This gives us the differential equation 

m = F„ + *[r(0 - At ^ 2 ], (19) 

whose solution is 

V(t) = - ^ |\ - A- 2 * e (1 “ *> - l)HkM) ]. (20) 

This equation is, of course, to be applied only 
for t — A t. 

From equation (20) we find that 



and 

V(At) = (1 + k) Vo, 

agreeing with the previously obtained results. 
The order of magnitude of the effect described 
above is seen to be quite negligible for the fuzes 

K 3 v 0 



t 


Figure. 2. Variation of voltage in fuze antenna; 
fuze and target stationary. 

described here. This effect may, however, take 
on fundamental importance for fuzes operating 
on other principles, such as those working on 
acoustic or pulse-time principles. 


2 ' 2 ' 4 Implications of Impedance Concept 

The advantage of regarding the basic effect 
of a reflector as an impedance change can be 
seen when an attempt is made to describe the 
phenomenon in terms of another concept which 

m 


appears at first plausible, namely, the concept 
of the effect of the reflection as a generator e 
in series with the radiation impedance Z llf as 
in Figure 3. The reflector does indeed create a 
voltage e in the antenna. This voltage e how- 
ever, changes the current I in the antenna, 
ivhich in turn changes e, and so on. This effect 
of the change in I upon e must be taken into 
account, and the impedance concept does this, 
whereas the generator concept as ordinarily 
applied does not do so; we do not ordinarily 
think of a generated voltage e as being affected 
by the current changes which it produces in the 
external circuit. Of course, in those cases in 
which the reflected voltage e is small enough so 
that its effect on / is negligible it may be treated 
as a generator. 

Another important aspect of the impedance 
concept is its essentially geometric character. 
It will be shown by more detailed analysis in 
the following sections that the reflected imped- 
ance in an antenna due to the presence of a 
reflector is a function only of the geometric 
configuration, of the directive properties of the 
antenna, and of the character of the reflector. 
The power level at which the antenna radiates 
has no effect on the reflected impedance ; 
this, of course, is not true of the reflected 
voltage. This lack of dependence of the re- 
flected impedance upon power level implies that 



Figure 3. Generator e in series with fuze 
antenna impedance, Z\\. 

fuzes with widely differing power outputs can 
be made which have the same sensitivity to 
reflection. This is indeed true ; fuzes have been 
made with radiated power outputs ranging 
from % mw to 1 w, with equal sensitivity to 
reflection. From the point of view of freedom 


SECRE 1 




22 


THE RADIATION INTERACTION SYSTEM 


from interference, however, it is fairly obvious 
that the higher power level is desirable. That 
is, the reflected voltage increases with the power 
level and therefore any extraneous radiation 
would have to be so much the stronger to in- 
duce, in the fuze, signals comparable in magni- 
tude to those coming from the reflector. 


2 3 MUTUAL INTERACTION OF SYSTEMS 
OF TWO-TERMINAL NETWORKS 
INVOLVING RADIATION 

In the preceding section it has been shown 
that, with certain approximations, the effect of 
a reflecting target is equivalent to a change in 
the input impedance of the fuze antenna. To the 
extent that this is so, the interaction phenom- 
ena between fuze antenna and target are de- 
scribable in terms of the steady-state analysis 
of coupled networks. The familiar concepts of 
mutual impedance and reflected or coupled im- 
pedance will be used. In fact the antenna imped- 
ance change to be evaluated is identical with 
the reflected or coupled impedance of circuit 
theory. 


2,3,1 Fuze Problem as Interaction of 
Two-Terminal Networks 

For fuzes of the single-antenna type, devel- 
oped by Division 4, the problem of the inter- 
action with the target reduces to that of com- 
puting the reflected impedance. The actual tar- 
gets encountered by the fuze radiation may be 
relatively simple, as in the case of ground ap- 
proach where the fuze can be considered as in- 
teracting with its image, or complicated, as in 
the case of an aircraft target with its compli- 
cated mode of excitation and complicated re- 
flection pattern. In the latter case it is custom- 
ary toftdetermine performance of a fuze on the 
basis of its interaction with a simple target, 
such as a half-wave reflecting dipole, and by 
experiment to relate the reflection from the 
complicated target to that from a simple target. 

Thus in the argument which follows in this 
section the problem will be set up on the basis 
of mutual interaction between a system of n 


simple two-terminal networks connected by ra- 
diation. In some cases one of these networks 
will represent the target antenna. When the 
theory has been worked out formally on this 
basis, the problem of a complicated target will 
be discussed in more detail. 


2 3 2 Fundamental Equations 

We now formulate the problem in a more 
precise way. Let the fuze and reflecting objects 
be considered as a system of antennas. If the 
ground is involved, we consider it as perfectly 
conducting and replace it by the image of each 
of the real antennas. For the fuze problem the 
fuze antenna and its image are driven ; all other 
antennas are parasitic. If some of the other an- 
tennas are driven by appropriate generators, 
we are then concerned with fuze operation in 
the presence of interference or intentional coun- 
termeasures. This case is subject to separate 
treatment, which is not within the scope of this 
volume. 

In general, if we have the fuze antenna inter- 
acting with 7i — 1 additional antennas, we may 
set up n equations : 

V\ — IiZn -f I2Z12 + I3Z13 + ' ' ' + InZin, 

V2 = I1Z2I + I2Z22 + I3Z23 + * ' * + InZ2n, ( 21 ) 


V n ~ IlZ n l + hZ n 2 + 1 3Z n 3 + ‘ ‘ * + I n Z n n, 

where 7 y is the current in the jth antenna and V s 
is the voltage impressed on the jth antenna. 
The set of equations (21) is a well-known way 
of representing the interaction between n cou- 
pled circuits or n antennas. On account of the 
reciprocal relations between antennas, Z ti = Z j{ . 

The meaning of the Z’ s can be elucidated 
quite simply. If, for example, we open-circuit 
all antennas except No. 1 so that all Us except 
/1 are zero, we have Vi = I,Z 1U so that Z 1X is 
the free-space impedance of antenna No. 1 and 
Vi and 1 1 are the free-space voltage and cur- 
rent, respectively. IiZ 2 i is the open-circuit 
voltage of antenna No. 2 due to current 7i in 
antenna No. 1. The term Z 2 1 is the mutual 
impedance between No. 1 and No. 2. The 
input impedance of No. 1 in the presence 
of an arbitrary number of other antennas is 


MUTUAL INTERACTION OF NETWORKS INVOLVING RADIATION 


23 


(Vi/Ii) = Zx. When the n antennas are too far 
apart to influence each other, the ZJ s vanish 
(i ¥= j) leaving only the Z u ’ s. 

As has already been mentioned, the ground 
is considered as a perfectly conducting plane, 
infinite in extent. Modifications required for an 
imperfectly conducting ground are considered 
later. It is well known that we may “remove” 
the ground plane and replace it by images of 
each of the antennas above ground. The rela- 
tion of the currents in an image and a real 
antenna are shown in Figure 4 for two con- 
figurations. The arrows point in the direction 
of instantaneous current. 

If the components of current normal and 
parallel to the surface are always as shown, the 
boundary conditions at the reflecting surface 
will be satisfied and the field of the image above 
the plane is identical with the reflected field. 

Since each of the images contributes to the 
total effect on the fuze antenna, they may ap- 
preciably affect the operation of the fuze. When 
the target and fuze are far removed from 
ground, the effect of their images becomes neg- 
ligible. This is essentially true of the applica- 
tion of the fuze against enemy aircraft in flight 
for fuzes as now constructed. The influence of 
the ground in this case will be discussed in 
more detail later. 

To take account of the effect of the ground 
we include the images in the set of n equations, 
letting the odd numbers represent real anten- 
nas and even numbers the image antennas. 
Thus antenna No. 1 represents the fuze, No. 2 
its image, No. 3 a real antenna, and No. 4 its 
image, and so on, each even number represent- 
ing the image of the odd number preceding. 

In the notation of equation (21) the bound- 
ary conditions will be satisfied if we put 

I r = -/ ( r- i) (r even). 

Since 

Z T = Z (r - i), V r = —V (r - !). 

It will now be found that the odd-numbered 
equations from equation (21) form a complete 
set of n/2 equations to specify the solution for 
the n/2 currents in the real antennas. The re- 
maining equations can be shown to form an 
identical set and so contribute nothing further. 


Specific Fuze Equations 

In the typical fuze situation only the fuze 
antenna is driven. In equations (21) this is rep- 
resented by putting V 1 = V and V 2 = — V with 
all other V i = 0. Let us consider this case and 
solve for V/I lf the apparent input impedance Z x 
of the fuze antenna. As previously stated, we 
use only the odd-numbered equations. 

A sufficiently general case which includes all 


REAL T REAL 

ANTENNA ANTENNA 

' 7/77 777 ^7777777 


< ■ IMAGE IMAGE 

Figure 4. Relation of currents in real and 
image antennas, for horizontal and vertical 
cases. 


fuze problems of immediate interest arises from 
the consideration of two real antennas and their 
two images. For this case antenna No. 1 is the 
fuze, antenna No. 2 its image, antenna No. 3 is 
the target, and antenna No. 4 is its image. 

For this special case the appropriate equa- 
tions are 

V = IiZn — I1Z12 + I3Z13 — IsZu 
0 = 1 \Z \3 — I1Z2Z + I3Z33 — I 3 Z 34 

where we have utilized the fact that Z if — Z jV 
By symmetry, it is clear that Z 23 — Z 14 . Incor- 
porating this in equations (22) we get for the 
input impedance Z x of the fuze 


v V _ „ v (Z 13 - Zu) 2 

"1 ^11 _ 12 77 7 , • 

Il 33 — Zj 34 


(23) 


Equation (23) shows that the impedance of 
the fuze antenna is its free-space value Z X1 plus 
additional terms representing the presence of 
target and ground. Three cases of interest arise. 

Case I. Ground Approach. In this case the 
fuze uses the ground as a target and antenna 
No. 3 with its image No. 4 are absent. This 
means that there are no nearby reflectors ex- 
cept the ground. For this case Z 13 = Zu = 0 
and Z 1 reduces to 


Z\ — Zu — Z12. 


(24) 


SECR 


24 


THE RADIATION INTERACTION SYSTEM 


The coupled impedance is the mutual impedance 
Z 12 between the fuze and its image. This leads 
to an important concept in understanding fuze 
operation against the ground ; i.e., in the 
ground-approach case the fuze can be thought 
of as being fired by its image. Since object and 
image are connected by a line normal to the 
plane, the vertical distance from fuze to plane 
is a determining factor. 

Case II. Isolated Airborne Target. It is now 
assumed that antennas No. 1 and No. 3 are far 
removed from ground in comparison with their 
separation. This makes 

Z12 = Z\\ = Z34 = 0. 

The result is 

Z, = Zn ~ f-, (25) 

Z/33 

and the coupled impedance has the value 
(Zi 3 2 /Zw). An interesting point should be men- 
tioned here in connection with jamming fuzes. 
If antenna No. 3 represents a jammer antenna 
instead of a target and if Z 33 includes some 
negative resistance incorporated by feedback 
of some sort, Z 33 can be made much smaller 
than the Z 33 obtained if the feedback is re- 
moved. Thus a negative resistance jammer will 
build up a signal of magnified form and may 
cause the fuze to function before it should 
normally. 

Such a scheme has difficulties of realization 
in practice which may make it impossible. 

Case III. Airborne Target ivith Ground In- 
terference. In this case the full equation (23) 
is applicable and must be considered in some 
detail. If the target is not moving with respect 
to its image, as in the case of a test target, Z 34 
will be a constant and reasonably small com- 
pared with Z 33 . To a good approximation we 
may use Z 33 alone. Thus equation (23) includes: 

1. Z 12 representing the interaction of the 
fuze antenna with the ground. 

2. Z ]3 2 /Z 33 representing the interaction of 
the fuze antenna with the target plus two other 
terms of the same order as this which may 
lead to interference. 

This is as far as the argument can proceed 
without detailed knowledge of the mutual and 
self-impedances involved. We now turn atten- 
tion to the values of impedance to be expected. 


2 4 ANALYTIC EXPRESSIONS FOR 
MUTUAL IMPEDANCE, RADIATION 
FIELDS ONLY 

2 41 Basis of the Argument 

We have developed above general expressions 
for the apparent input impedance of the fuze 
antenna when in the neighborhood of other 
antennas, among which may be included the 
image of the fuze antenna. These equations will 
now be made more specific, so that they can be 
applied to actual cases. 1 ’ 4 * 9 

In the argument to follow we will confine our- 
selves to the case of radiation fields alone, leav- 
ing the problem of correction due to induction 
and quasi-static components to Section 2.10. The 
corrections are not necessary to predict fuze 
operation in a large majority of cases. 

By neglecting the corrections it is possible to 
set up a general argument which makes no as- 
sumptions about the nature of the current dis- 
tribution on the fuze antenna or the mode of 
interaction with the reflected radiation. All we 
need to know about the fuze antenna is that: 
(1) it has two terminals for connection to the 
oscillator circuit; (2) when current flows 
through these terminals, radiation appears in 
the surroundings with a distribution which can 
be measured experimentally; and (3) the loss of 
energy by radiation appears as a resistance in 
the antenna circuit to which the oscillator is 
connected. 

To derive the necessary expressions we will 
first express the field strength E of an antenna 
at point P in space in terms of (1) the distance r 
from the antenna, (2) the experimentally meas- 
ured radiation pattern /(0,</>), (3) the gain G 
of the antenna as calculated from (4) 

the series radiation resistance R s , and (5) the 
driving point current I into the antenna ter- 
minals. 

The meaning of R s may be clarified by repre- 
senting the system as in Figure 5, where the 
box is the fuze system which emits radiation. 
If we integrate the energy flow at infinity when 
a current I flows into the terminals, we find that 
a certain amount of power is carried away by 
radiation. If this power is W, then by definition 
2TU 2TT 

tls |JJ2 0r JJ*' 


FORMULAS FOR MUTUAL IMPEDANCE, RADIATION FIELDS ONLY 


25 


Now there may be other components in the box 
which dissipate energy. They are not included 
in R s . 

If we measure the input impedance at the 
terminals TT when the box is in free space in 



Figure 5. Representation of fuze system emit- 
ting radiation. 


the absence of reflectors, the result is Z u . When 
reflectors are present, the result is Z u as defined 
previously. The above definition of R s implies 
that all the antenna current I flows through R s , 
meaning that R s is in series with I. Likewise 
the coupled impedance representing the reflec- 
tor will also be in series with I. The argument 
upon which equations (21) are based then 
means that we consider the antenna as equiv- 
alent to the circuit in Figure 6. Thus Z X1 — R s + 
R a + jX 8 and A Z represents the reflected im- 
pedance. The term R a represents the ohmic 
losses in the antenna, which are quite small and 
will be neglected unless otherwise specified. 

When the field relations have been derived, it 
will then be necessary to determine the response 
of the antenna to radiation falling upon it. This 
will be derived with the aid of the reciprocity 
theorem. The two concepts will serve to solve 
the fuze problem in so far as pure radiation 
fields are concerned. 


Field Equations for Arbitrary 
Antenna 

We assume a spherical coordinate system, 
with the origin at the center of the antenna 
and the antenna lying along the polar axis. The 
electric field strength E is a vector function of 
position. If we describe a large imaginary 
sphere around the antenna, then a plot of the 
field strength E, on the surface of the sphere, 
as a function of the polar angle and the azimuth 
angle <f> is known as the space radiation pat- 
tern of the antenna. If we normalize the values 


of \E\ found around the sphere so that the 
maximum value is unity, the dependence on 
6 and <£ is known as The actual value 

of the field strength at any point ( 0,<f > ) on the 
sphere is given by 

\E\ = £ 0 /(W), (26) 

where E 0 is the maximum value of \E\ on the 
surface of the sphere. We assume that /(0,<£) 
has been determined experimentally (see Sec- 
tion 2.8) . 



Figure 6. Series equivalent circuit of fuze 
antenna. 

The power W radiated through the sphere is 
obtained by integrating the Poynting vector 
over the surface of the sphere and is given in 
mks units by 

2jt n 

w = r ¥o f f p ( ®**> sin md4, (27) 


where 


W 


Ed 2 f 2 
2Z 0 


(28) 


2tt 7 r 

f f r si 


sin dddd(t), 


and 


Z o = V (mAK), 

the “intrinsic impedance” of free space, \i and K 
being the permeability and dielectric constant 
respectively of free space, or air. The term 
Z 0 = 120t r ohms. 

Taking into account equations (26) and (28), 
we write 

E = \ {/(0,4>y M ■ <2 ” /X)1 }, (29) 

where l is the wavelength. This expression ig- 


SECRET 


26 


THE RADIATION INTERACTION SYSTEM 


nores a possible additive phase shift which may 
be a function of It will be introduced 

when needed. 

We may now introduce the concept of gain 
of an antenna. If we compare two antennas, 
each of which radiates so as to produce equal 
values of E 0 at a given distance r, then the an- 
tenna which radiates less power has the greater 
gain G. An antenna for which the space radi- 
ation is spherical, i.e., one which radiates 
equally in all directions, has the lowest possible 
gain. From equation (28) we see that for two 
antennas, No. 1 and No. 2 , with equal values 
of E 0 at the same value of r 


G* _ Wi _ 7i 

Gi W 2 72 


(30) 


For an isotropic radiator y = 4 tt. If we arbi- 
trarily assign this antenna a gain of unity, we 
have for any antenna 


G 


4 7T 
7 ' 


(31) 


Typical values of G for representative antennas 
will be found in Figures 21 through 24. 
Equation (29) may now be transformed: 


E = \ - (2 " A)1 }- (32) 

As already indicated, we put 

R a = JJJ 2 , ( 33 ) 

and rewrite equation (32) as 

E = 7 ypff- {m^V C - 2 ' rA) } ( (34) 

where G = |/| e ,ut . The factor j correctly re- 
lates the phase of E to that of h in the case of 
an elementary dipole. For other antennas, there 
may still be an additional phase shift, as men- 
tioned above. This is the final equation relating 
the field to the antenna and shows the radiation 
field as a function of position around the fuze 
antenna. To solve the fuze problem we need to 
know how this arbitrary antenna responds to 
fields as a receiver. A discussion of the problem 
follows. 


2 43 Mutual Impedance Between Two 
Arbitrary Antennas 

In the following discussion we assume that 
the radiation is in the form of plane waves. 
This in effect means that the absolute value of 
the field does not vary over the length of the 
antenna for distances at which we are inter- 
ested. 

We know that a current in one element sets 
up a voltage in another. These may be coupled 
by radiation, in which case the radiation field 
from one antenna carrying current h generates 
a voltage in the other and we mgy say that the 
impressed field on an antenna generates a volt- 
age at its terminals. Since the antenna is a 
linear circuit element, we can say that the volt- 
age at its terminals is proportional to the field 
intensity acting upon it. If this field varies 
along the antenna, it will be necessary to pick 
some reference point in space and say that 

V = IE, (35) 

where E is the value of the field at this refer- 
ence point and l is a constant of proportion- 
ality having dimensions of length, usually called 
the effective length. The term V is the open- 
circuit voltage at the antenna terminals. It is 
customary to select the feed point of the an- 
tenna as the reference point. If this is done, 
E will then represent the field intensity at this 
point in space if the antenna is assumed to be 
absent while the field intensity is determined. 

Now consider two arbitrary antennas, No. 1 
and No. 3, like those treated in Section 2.4.2, 
separated by distance r with currents h and / 3 
at the feed points. Assume that h gives rise to 
a voltage V 3 at the terminals of No. 3 when / 3 
is zero, and assume that / 3 gives rise to a volt- 
age V 1 at the terminals of No. 1 when h = 0 . 
By means of equations (35) and (34) we can 
write 

J' 3 = h - 1 yj ~] ^ Vi^, <£ 13 ) (cos r)je A 2 ’ rr/X) , 

(36) 

Vi = h £ (cos r)je“ 

Here we introduce the angle x to take account 
of any skew relation between the two antennas. 


ANALYTICAL FORM OF REFLECTED IMPEDANCE 


27 


Here fi( 6 13 y <f>i 3 ) denotes the value of f(O y <f>) 
for antenna No. 1 in the direction joining the 
fuze and target antennas No. 1 and No. 3 re- 
spectively, and f 3 ( 0 31 y <j> 31 ) has an analogous 
meaning. 

At this point we shall call upon the Rayleigh- 
Carson reciprocity theorem. The statement of 
this theorem as given by Carson is as follows : 95 

“Let an emf E /, inserted in any branch, des- 
ignated as No. 1, of a transducer, produce a 
current / 2 ' in any other branch, No. 2; corre- 
spondingly, let an emf E 2 " inserted in branch 
No. 2 produce a current //' in branch No. 1; 
then I/'E/ — I 2 'E 2 ".” 

A transducer is defined as “a complete trans- 
mission system which may or may not include 
a radio link, which has accessible branches, 
either of which may act as the transmitting 
branch while the other acts as the receiving 
branch.” 

The theorem of reciprocity applied here 
means that 


F 3 Vi „ 

T = T = Zl3 

O 1 3 

= l j (COS r )je* ~ 2 " A) . 

(37) 

Equations (36) and (37) give 

h /i (^13,013) = h °4^ 3 3 f 3(031, <f>n)j 

(38) 


or 


h _ h 

IZqRssGs , f \ Iz 0 r s iG l { , \ 

V — 4 ^ — j 3(031,931) yl — ^ JlWl3,<Pl3; 

Thus for any antenna we may write 


l 




ZqR 8 G 


M+) 


= c 


(39) 


(40) 


where C is a constant not involving any of the 
variables in equation (39). Finally 


l = C 



(41) 


showing that as a receiver the antenna behaves 


the same as a transmitter in its dependence on 
Z 0 R s , G, and 

The mutual impedance between two arbitrary 
antennas can now be expressed. Antenna No. 1 
impresses a field on antenna No. 3 as given by 
equation (34) ; antenna No. 3 receives it with 
an effective length l 3 given by equation (41). 

7 V3 GEl CZ 0 /~d e > p ri 

^13 ~ ~T ~ ~f — — ~ A V .tt s i/£ S 3CriCr3 • 

1 1 1 1 4 TTf 

/i( 013,<M /3(031,03l) (cos r)je j ( - 2vr/x \ (42) 

If we can evaluate the constant C for any two 
antennas, we have it for all antennas. In Sec- 
tion 2.14 it is shown that C has the value 
(2k/ Z 0 ) . Inserting this into equation (42) gives 


Z13 — 2 ^ a / RslRssGiG 3 fi(du, 4 >u) 


f 3 ( 631 , <t> 3 i) (cos r)je j ( “ 2irr/x) . (43) 


Equation (43) represents the mutual imped- 
ance between two arbitrary antennas separated 
far enough so that the radiation field (1/r term) 
is the only one of importance. 

We have seen in Section 2.3 that the antenna 
impedance of the fuze in the presence of reflect- 
ing targets can be represented as the sum of its 
self-impedance in free space plus terms in- 
volving mutual impedances Z {j and the self- 
impedance of the reflectors. Equation (43) 
gives the analytic form of the mutual imped- 
ances Z ijy if 1 and 3 be replaced by i and j, 
respectively. 

We are now in position to apply this general 
formula to special cases representing a fuze 
approaching ground (interacting with its 
image) or a fuze approaching an airborne tar- 
get well away from the ground. 


2 3 ANALYTICAL FORM OF REFLECTED 
IMPEDANCE 9 

The analytic expression equation (43), de- 
rived in the preceding section, will be applied 
to three special cases and appropriate working 
formulas discussed. The general properties of 
the reflected impedance common to all three 
cases will then be discussed. 

b Bibliographical references pertinent to this section 
are 1, 13, 16, 17, 22, 27, 51, 53, 93. 


secretI 


28 


THE RADIATION INTERACTION SYSTEM 


The general equations for the total antenna 
impedance of the fuze discussed in Section 2.8.1 
were applied to three special cases with the 
following results : 

Case I. Ground Approach. 

Z ! = Z n - Z 12 . (24) 

Case II. Airborne Target Far From Ground. 

Zx = Z n - (25) 

Case 111. Ground Interference Case. 

Zx = Zxl - Zx 2 - ( f 13 ~ y u) ' . (23) 

6 33 — ^34 

Each of these equations is of the form 

Z\ = Zn — Z r , (44) 

where Z v represents the reflected impedance. 
The vector interpretation of this equation has 
already been given in Figure 1. 

Ground-Approach Equation 

A fuze approaching ground, in the absence of 
other reflectors, is interacting with its image 
and Z r — Zi 2 . Furthermore, since antenna No. 2 
is the image of antenna No. 1, we see that 

Rsl = Rs2) 

Gi = G 2 , 

fl (012,012) = f2 (021, 02l), 

T = 0 , 

r = 2h (h = height above ground). 

Introducing these relations in equation (43), 
we have 

Zr = Zxx = ^ GR.fi 2 (0,2 ,0, s )je ( -*'*A). (45) 

Equation (45) gives the detailed form of Z r 
for approach to a perfectly reflecting ground 
of large extent. As in equation (29) and sub- 
sequent equations a possible additive phase 
shift is ignored. From the results obtained in 
the case of the perfect reflector, we may ex- 
trapolate to actual grounds (plane reflectors) 
by the use of a reflection coefficient n. For pur- 
poses of these applications, the effective reflec- 
tion coefficient n for a given surface is defined 
in such a way that the signal magnitude re- 


ceived by a fuze circuit, because of the presence 
of the surface, is n times the signal that would 
be received from a perfect reflector in the same 
position as the actual reflector. 

This definition was set up to avoid possible 
errors in using the reflection coefficients de- 
rived for plane waves on the classical theory. 
(The equiphase surfaces of radiation from the 
fuze antennas have appreciable curvature at the 
usual distance of interest in fuze applications.) 
As a matter of fact, however, it has been found 
that the values of n found according to the 
above definition agree well with the published 
values of n based on the plane wave theory and, 
to the accuracy needed for fuze calculations, are 
independent of the height above the ground. 
Additional comments regarding n are to be 
found in Sections 2.9 and 2.14. 

The reflection coefficient n has been measured 
by moving a fuze over a perfect reflector then 
over ground and comparing results (see Sec- 
tion 2.9) . 

When the reflection coefficient is included, 
we have 

Zr = l ^ GRs fl 2 (0 i 2,0 i 2 )^(-> 4 ^/x). (4 5a ) 


Airborne Target Equation 
For target and fuze a long way from ground 



With the aid of equation (43) we get 
* ■ -&)'■ 

^ S lfis3b ? lG ? 3 /l 2 (013,013)/3 2 (031,03l)CQS 2 T ^ -j^ r/ \ ( 4 Q) 

Z33 

Equation (46) is limited in its application to 
cases where the target can be considered as a 
single antenna with a single feed point. Thus it 
represents the case for a dipole reflector or a 
strip of “window.” If the target can be repre- 
sented as an array of simple antennas, then Z, 
would involve mutual interaction with the whole 
family, including terms arising from the mutual 
interactions between members of the array. 

If the target is not made up of linear anten- 


SECRET 




ANALYTICAL FORM OF REFLECTED IMPEDANCE 


29 


nas but is a geometric shape capable of excita- 
tion in a complex manner, equation (46) cannot 
be used as it stands, since it is obvious that we 
cannot cut a complicated target arbitrarily and 
reproduce its complicated current distribution 
by feeding it at one point. 

If we knew the current distribution on the 
target arising in response to the radiation from 
the fuze, we might proceed as follows: (1) find 
the number and location of the feed points nec- 
essary to reproduce this distribution, (2) deter- 
mine for the target when excited by 

each feed alone, (3) treat each feed with its 
f as a single antenna, (4) measure the 
mutual impedance between feed points, and 
(5) proceed with the general equations (21). 
For any ordinary target such a process is im- 
possibly complicated, and we resort to more 
tractable methods. 

Again we assume the fuze and the target to 
be far enough apart so that we can consider the 
fuze radiation to consist of plane waves at the 
target. We then determine the reflecting power 
A of the target as follows: (1) We irradiate 
the target with plane waves with a field inten- 
sity E if and (2) we measure the field E r reflected 
back along the direction of the incident radi- 
ation. If this field E r is measured at distance r 
from the target, A is defined by 

E r = ^4 (47) 

The (1/r) dependence of E r is consistent with 
our initial assumptions concerning the plane 
waves from the fuze. Note that A has the di- 
mensions of a length. 

For a single linear antenna, it follows from 
the definition of A that A for such an antenna 
is given by 

A = 2 ^ G 3t /* 3 2 (0 3 i,$ 3 i) cos t. (48) 

As an example, consider A for a resonant half- 
wave reflecting dipole oriented for maximum 
reflection. In this case R s 3 = Z 33 ; G 3 = 1.64, 
/ 3 2 = 1 cos x = 1, and A 3 = 0.26. Typical 
values of A for other simple reflectors are given 
in a paper by Mott. 93 In particular, 

A (sphere) = Ja, where a is the radius of the sphere; 

Z/2 

A (flat sheet) = — where L 2 is the area of the sheet. 

A 


We now express Z r in terms of A as defined 
above with the aid of equation (48) and get, 

Z r = A ~ fl.A/i 2 (0„,<fo s ) (cos (50) 

For each antenna, x is the angle between the 
plane of polarization of the incident radiation 
and the plane formed by r and the axis of the 
antenna. 

If the antenna is a complicated structure, 
the meaning of A in equation (50) will require 
modification to include effects of the twisting 
of polarization of the incident radiation. 

In the case of an actual aircraft target it 
would be necessary to know A at all angles, 
since the fuze sees a continually varying aspect 
as it approaches the target. Thus the calcula- 
tion of Z r by the use of equation (50) would 
require analytic expression of A as a function 
of direction toward the fuze. 

The necessary information can be achieved 
in a more expeditious manner. An actual fuze 
is set up and the target moved past it slowly 
while the signal in the fuze is recorded. The 
recorded wave can be reproduced and used 
directly for testing fuze circuits. Such experi- 
ments are described in detail in Section 2.11. 

To relate these measurements with our cal- 
culations the strength of the reflection was com- 
pared with the reflection from a resonant half- 
wave dipole, which can be computed directly 
from equation (46), giving 

Z r = 0.042^y R al GJ{ 2 (0,3,<*«i3)e- jW \ (51) 

for the dipole orientation which gives maxi- 
mum reflection. 

In general we find that the maximum reflec- 
tion from the aircraft as it passes the fuze is 
N times the reflection from a dipole given by 
equation (51). It has the same dependence 
upon distance as a dipole for approaches that 
are not too close. The term N will not be a con- 
stant for a given target but will depend on A. 

From Mott’s paper 93 we find that A for a flat 
sheet of area L 2 is L 2 /A, and A for a dipole is 
0.26A. Thus, a sheet of area L 2 is the equivalent 
of N dipoles, where 

„ 3.88L 2 

A 2 ' 


(49) 




30 


THE RADIATION INTERACTION SYSTEM 


With the aid of equation (51) this shows that 
Z r is independent of \ for the case of a flat sheet. 


253 Ground Interference 

The general equation covering this case for a 
fuze and one target is given by equation (23) : 

Zi = Zn - Zn - ( y 13 ~ y“ )2 . (23) 

The detailed treatment of this case for a 
complicated target is beyond the scope of this 
report. However, certain general properties can 
be observed. 

The symbol Z r consists of two terms, the first 
representing the reflection from the ground and 
the second the reflection from the target, in- 
cluding the effect of the images. Now, in gen- 
eral, Z 34 is small compared with Z 33 ; it will be 
10 per cent or less for a dipole if the separation 
is 4 l or more. Thus we may write Z r as 

7 7 , (Zu ~ Z U ) 2 

Zj r ~ Zri2 ~\ , 

^33 

with reasonable accuracy in so far as absolute 
magnitudes are concerned. 

When the distance between antennas No. 1 
and No. 3 is large compared to the distance 
between No. 1 and No. 2, |Zi 3 | is nearly equal 
to \Z 14 \ and the effect of the target is compli- 
cated by phase relations between Z 13 and Z i4 , 
giving rise to interference in the reflection 
which may be quite pronounced. However, when 
the fuze gets close to the target, or when the 
distance from fuze to target is much less than 
the distance between target and ground, Z u and 
Z 12 are small, and the signal is approximately 
equal to the free-space signal. 

The situation is further complicated by the 
directional properties of target and fuze. In 
each impedance Z ijt f(6,<j>) must be evaluated 
in the direction (0^,0^) from each antenna. 

Any further discussion must be limited to 
special cases. One particular example is of in- 
terest. Neglecting directional factors, we com- 
pare the strength of the reflection from ground 
with the reflection from a resonant half-wave 
dipole oriented for maximum reflection to the 
fuze. We wish to determine at what distance r 


from a dipole the reflection is the same as from 
the ground at distance h. 

From equations (51) and (45) \Z 12 \ = \Z 13 \ 
when 

0.042^/^ (ft,,*.) = |^/i 2 (012, <M. 

Now if the radiation pattern of the fuze be such 
that 

fl 2 (013,</>13) = /l 2 (012,012), 

then the signals are equal when r = V 0.52 \h. 
If X is about 10 ft and h is 10,000 ft, then r = 
230 ft. 

In the early days of fuze design this limita- 
tion caused some needless concern. In the first 
place the reflection from an airplane is of the 
order of 10 times that from a dipole. In the sec- 
ond place the radius of action of practical fuzes 
described in this volume is about 75 ft. In the 
third place the orientation with respect to the 
ground and the relative motions involved make 
the ground signal less important. 

Only in special cases where the fuze is used 
against airborne targets near the ground does 
the ground reflection become a limitation on 
fuze operation. 


254 Special Considerations of Transverse 
Antenna Fuze 

In the preceding discussion it has been as- 
sumed that the fuze can be represented by a 
single antenna. This applies for fuzes using the 
missile as the antenna. In the cases of fuzes 
with transverse dipoles as antennas (T-51 and 
T-82), the expected variations of antenna im- 
pedance are complicated by the presence of the 
body of the missile near the fuze antenna. If the 
transmitter and receiver circuits are not elec- 
trically and mechanically balanced with respect 
to the missile, longitudinal currents are excited 
in it and these radiate energy. As a result there 
is in effect an additional antenna in the system, 
and its contribution to the performance of the 
fuze must be considered. Furthermore, even if 
perfect balance is obtained, the missile serves 
as a director or reflector behind the fuze to alter 


ANALYTICAL FORM OF REFLECTED IMPEDANCE 


31 


its sensitivity pattern (see patterns in Section 
2.8). We are not here concerned with this latter 
effect. We are concerned with the results of in- 
cidental unbalance that arises in the manufac- 
ture of fuzes. 

To study them we idealize the system as two 
thin antennas arranged at right angles and con- 
cern ourselves with the reflected impedance Z r 
when this system approaches the ground. To 
the extent that we can represent the system by 
two thin antennas the general arguments of 
Section 2.8 can be applied. 

The arrangement to be considered is shown in 
Figure 7. « 



GROUND PLANE 



Figure 7. Representation of transverse dipole 
and projectile, with their images. 


Antenna No. 1 is the fuze antenna. This case 
was treated in Section 2.3 for another purpose 
and led to equation (23), which is 

Zl = Zn - Z n ~ ( y 3 ~ | h)2 . (52) 

Z/33 — Z/34 

To interpret this equation we expand and get 


Zi = Z 11 


Z 3 
+ 2 


3 — Z34 

ZnZu 
Z 33 — Z 3. 


Z33 — Z 3, 


(53) 


The first two terms of equation (53) represent 
the interaction of the T-51 or T-82 fuze with 
its image in the absence of any vehicle. Z ri rep- 
resents the free-space impedance and Z 12 the 
reflected signal. This has been generally inter- 
preted as the actual working signal in the T-51 
fuze when used. If the balance is perfect, 
Z 13 — 0 and equation (53) reduces to 


which shows that even though the projectile is 
not excited directly by the fuze antenna it 
nevertheless contributes to Z r . In general Z M is 
small compared to Z 33 and serves to modulate 
the second-order reflection terms. We will neg- 
lect it in comparison with Z 33 in the remainder 
of the discussion. Also we may use Z 33 and Z 4 4 
interchangeably, since they are images of each 
other. The term (Zi 4 2 /Z 44 ) represents the re- 
flection from the image of the projectile as a 
target for the fuze antenna. 

To discuss the problem further we need a co- 
ordinate system. We choose the z direction as 
the axis of the missile with x and y axes per- 
pendicular to it, the x axis being the axis of the 
transverse dipole. We also choose a as a polar 
angle. It is the angle between z and the normal 
to the ground, that is, the striking angle of the 
projectile referred to the vertical. The term 5 
is an azimuth angle measuring the angle be- 
tween the x axis and the plane including the 
axis of the projectile and the normal to the 
ground (plane of incidence). To estimate 
the order of magnitude of this effect we shall 
make the further assumption that antenna 
No. 3, representing the projectile, is a resonant 
half-wave antenna. We shall also consider the 
radiation pattern of such an antenna to be 
f(0) — sin 6, when 0 has the meaning pre- 
viously assigned ; this is a good enough approx- 
imation to the true pattern for this argument. 

The field components from the x-axis dipole 
will be 

E r = 0, 

E a = ki cos a cos 8, (55) 

E 8 = ki sin 8, 

where 


*1 = 7 A. (56) 

The component E a will be in the vertical plane 
containing antenna No. 4 and will give rise to 
a voltage in it. The term E& will always be per- 
pendicular to the plane and will produce no 
voltage in antenna No. 4. Thus Z 44 will be 

„ _ Eg U 

•£14 — j , 


Z\ — Zn — Z 12 — ~ 14 7 , (54) 

Z/33 — Zj 34 


h 

h 


U COS a COS 


5, 


(57) 


SECRET 


32 


THE RADIATION INTERACTION SYSTEM 


or 


. 2A IRsiGi RsaGi . 

Z 14 1 = — ^ — - j — cos a COS o sin a . ( 08 ) 

We then find 

4A 2 R s iGiGa •> s • 9 /-n\ 

/ r cos - a cos - 5 sin - a . ( o 9) 
r 2 (4 tt) 2 

when we assume the projectile is resonant, so 
that R s 4 = Z 44 . This will give rise to a change 
(Z,.) 4 1 in antenna impedance in antenna No. 1 
given by 



= RsiGiGa cos 2 a cos 2 5 sin 2 «. 
47 rr 

(60) 

We compare this with the so-called normal im- 
pedance change 

i Zu \ = RsiGi (1 — sin 2 a cos 2 5). (61) 

27rr 

The worst case we will be interested in will be 
8 = 0, a = 45 degrees, and 



|Zl2 I = 2 Vr R,lGl> ’ (62) 

l(Z r )i\ = R,iGiGi. (63) 

The signals arising from Z 12 and (Z r ) 4 will 
have an unknown phase relation depending 

upon striking angle and the size of the pro- 

jectile. We consider the worst cases where they 
may be in or out of phase. The interference will 
change the response by the ratio 

(A/47rr) G, ± (\ 2 /167rV 2 ) G 1 G 4 1 . 0.13A 

(X/4irr) G 1 1 ± “• (64) 

For heights of operation of r = 10A (that is, 
h = 5A) the maximum change in reflected sig- 
nal will be approximately ±1.3 per cent. For 
other angles a < 45 degrees, 8 0 degrees, the 

correction will be less, being 0 for 8 = 90 de- 
grees and all values of a. 

We thus conclude that the variations in height 
of burst from the source are small for a per- 
fectly balanced transverse antenna. 

A greater source of error is the unpredictable 
value of 8. For a = 45 degrees the reflected sig- 
nal changes from 1 to % as 8 varies from 90 to 
0 degrees. 

We now turn our attention to the correction 


arising when the antenna is not perfectly bal- 
anced. In this case Z 13 ^ 0. There will be two 
terms of interest. 


4 - Zl * 2 

Z 33 ' 

(65) 

D 2 ZuZu 

B = 7 • 

" 33 

(66) 


The term A is a fixed term independent of 
r or h and shows merely the amount of reflected 
impedance in antenna No. 1 by virtue of its ex- 
citation of antenna No. 3 by some unbalance. 
This term, being constant, will give rise to no 
signals. It is merely a measure of the coupling 
between antenna No. 1 and antenna No. 3. 

The term B gives rise to an additional signal. 
As before we will consider only absolute values 
and disregard relative phases, since the abso- 
lute values will indicate the maximum value of 
the corrections that may arise. 

To estimate the coupling we note that IiZ 14 
represents the free-space voltage at antenna 
No. 1. If Z 13 is small we can say also that hZ ls 
represents the voltage coupled into antenna 
No. 3. We define k by the relation 


7 \Z\ 3 


Z 13 

IiZu 


zli 


Experiments have shown that k is of the 
order 0.01 for well-balanced fuzes and may be 
as large as 0.1 for very poor balance, so poor in 
fact that the arrangement would never be used. 
These values are based upon the center point 
of the parasitic antenna as the reference point. 

Now 'Z n | is about 300 ohms and |Z 33 j >73 
ohms. Hence |Z 13 | is approximately 3 ohms and 


1 B 

JX3 

Z14 

— ft nor pont rvf 

Zi 4 

I Z \ 2 

- 73 

Z12 

O Lcll t DI 

Z 12 


For all angles of approach that are of interest 
|Zi 4 j < Z 12 1 so that the correction is less than 
10 per cent. If the unbalance becomes large this 
correction becomes sizable and can lead to a 
considerable change in function height. In most 
cases the projectile is nonresonant and |Z 33 | is 
considerably greater than 73 ohms. Thus inci- 
dental unbalance is not so important when the 
projectile is nonresonant. When resonance is 
approached the response becomes critical to 
unbalance as has been experimentally observed. 


SECR 


ANALYTICAL FORM OF REFLECTED IMPEDANCE 


33 


2,5 5 General Properties of the Reflected 
Impedance 


We are primarily interested in the two basic 
equations, the ground-approach equation and 
the airborne-target equation. We repeat them 
here for convenience. 


47 rh 


GJts.Pidn, * 12 ) 

(ground approach) , (45) 


and 


RsiG&i* ( 013 , *18) (cos T )e-**'A 

Z7rr z 

(airborne target), (50) 

or in alternative form for a linear antenna re- 
flector 


(cos 2 

Zaa 


(46) 


It should be remembered that the phase factor 
should carry an undetermined constant phase 
shift, related to the antenna properties of tar- 
get and fuze. 


f 2 ( 0 ,*) . Thus the radiation patterns become 
characteristic of a given vehicle, and R s can be 
adjusted to match the transmitter properly 
with the assurance that R s will have little effect 
on Z r /R s . 

A particular example is most enlightening. 
For antennas whose length lies in the range 
0 X/2, G varies from 1.5 to 1.64, about a 10 

per cent change. The term / 2 ( 0 ,c/>) in the 
worst direction only differs by 15 per cent in 
the two extreme cases. Thus the quantity 
Z r /R s is practically independent of antenna 
length in this range. On the other hand, R s 
varies from 73 ohms for a half-wave antenna 
to zero [as (LA) 2 ] for short antennas, where 
L is the length of the short antenna. We can 
thus state generally that all fuzes, whose re- 
sponse to a fixed value of (Z r /R s ) is the same, 
will have practically the same response to a 
given target no matter what the length of the 
fuze antenna is, provided it is considerably less 
than a half-wave long. The statement is also 
true for all loop antennas whose dimensions 
are small compared with l. 

For longer antennas / 2 ( 0 ,*) is sensitive to 
l, and each must be considered as a special case. 


Doppler Frequency 

As seen in Section 2.2 the phase has a fre- 
quency F = (2v/l), if | ( dh/dt ) | or j ( dr/dt ) j 
be replaced by v. This is identically the doppler 
frequency. 

Dependence upon R s 

Let us write R s for R s i. We note that Z r is 
proportional to R s , as would be expected, since 
it is the power dissipated in R s that accounts 
for the radiation fields which make the inter- 
action possible. 

It will be observed in a later section that the 
dimensionless quantity (Z r /R s ) is most con- 
venient for assessing fuze circuit response. It 
exhibits the effect of a reflector as a fractional 
change in antenna impedance which depends 
only upon the nature of the target and the 
directive properties of the fuze antenna (which 
are relatively independent of R s ). 

It has been found experimentally that small 
changes in the antenna feed point can change 
R g over a wide range with almost no effect on 


Dependance on Distance 

The magnitude of (Z r /RJ depends upon the 
distance through the dimensionless ratio 
r/l or h/l. This means that 1 is a scale factor 
in determining fuze performance. Response to 
the presence of a target is determined by the 
number of wavelengths in the distance to the 
target; thus, for example, the signal received 
from ground reflection at a given height is 
greater for greater a. 

Dependence on Direction to Target : 
Definition of Directivity 

The size of Z r /R s is proportional to Gi/i 2 
(0i3, * 13 ). Now Gi is a constant for a given 
fuze so that /i 2 ( 0 ,*) tells how well a fuze 
“sees” targets in various directions. The term 
/i 2 ( 0 ,*) is the power radiation pattern of the 
fuze antenna ; it is called the directivity pattern 
in this report. A plot of / 2 ( 0 ,</>) will show 
(other things being equal) the distance at 
which a fuze will function upon approach to a 
target. 


SECRET 


34 


THE RADIATION INTERACTION SYSTEM 


Now it will be observed that 

GJiKtaju) = Wu _ F(e i 3 ,<t>n), (67) 

47T W 

where JE 13 is the power radiated per unit solid 
angle in the direction (^ 13 ,^ 13 ) and W is the 
total power radiated. Thus F( 0 i 3 ,<£i 3 ) repre- 
sents the fraction of the total power radiated 
per unit solid angle in the direction (# 13 , <£ 13 ) • 
Thus f 2 (Ois,<fnz) is an indication of how effi- 
ciently the total radiated power is used. 

Typical directivity patterns are described in 
Section 2.8. 

Independence of Power Level 

It is clear, as was anticipated in Section 2 . 2 , 
that Z r /R s does not depend upon the power level 
at which the fuze radiates. 


26 CIRCUIT RESPONSE TO ANTENNA 
IMPEDANCE MODULATION 


Series and Parallel Expressions 
for (Z t /Rs) 


Differential Signals 

The foregoing analysis has been based upon 
the concept of series antenna resistance and re- 
actance. In actual cases, however, it is often 
more convenient to deal with the equivalent 
parallel quantities. We therefore proceed to de- 
rive expressions for the changes in parallel 
antenna resistance and reactance due to a re- 
flector. 

We deal with the two circuits in Figure 8 . 
The terms and \X 8 , or \X V and A R p , are the 
changes in antenna resistance and reactance 
resulting from the presence of a reflector; R p 
and X p , or R 8 and X H , are the free-space values. 

It is easily shown that in the absence of the 
incremental quantities we have 


R P 


X 


V 


Rs 2 + X 8 2 
Rs 9 


Rs 2 + X* 2 
X 8 ' 


( 68 ) 

(69) 


consider the differentials of R p and X p as equiv- 
alent to their increments. 

Then 

dR„ = || (RS - X, 2 ) + Jr (2 S,R,), (70) 

and 

dX p = dR, + ~ s (X, 2 - R?). (71) 

By defining Q = X 8 /R s and by appropriate 
manipulation we find 

dR p _ dR s (1 - Q 2 \ dX s ( 2 Q \ 

' Rp ~ Rs\ 1 + Q 2 ) ^ Rs \l + Q 2 )’ V ; 
and 

dX p 1 r dR s • 2Q dX s (Q* - 1)1 , 

Q [^(1 + Q 2 ) R S (Q 2 + 1) J* 

Now as we have seen, dR s and dX s are the 
components of a vector Z r which may be writ- 
ten as 

Z r = \Z r \e*, a = (74) 

where x represents the distance r or h from 
fuze to target. The term 8 depends on the par- 



SERIES CIRCUIT PARALLEL CIRCUIT 

Figure 8. Series and parallel equivalent fuze 
circuits. 


ticular case being discussed, but is unimportant 
for our present purposes. It will be found con- 
venient to use the dimensionless ratio ( Z r /R s ) 
which we define as a new vector M and write 

M= M 0 e ja , 

where 


For small increments of impedance we may 


(75) 



CIRCUIT RESPONSE TO ANTENNA IMPEDANCE MODULATION 


35 


If we define an auxiliary angle (3 by the relations 
1 - Q 2 


sm 0 = 


cosjS = 


1 + Q v 

2 Q 


l + Q r 

We can rewrite equations (72) and (73) as 


TT 2 = M 0 sin (a - /»), 

xL p 

dX p M o / Q \ 
T7 “ -Q cos (a - 


(76) 


(77) 


For purposes of convenience, it may be de- 
sirable at times to work in terms of the admit- 
tance Y, which is defined through the relation 


Y = 

Y = 


R s + jX.’ 
R s 

Rs 2 + X s 2 

Y = G — jB, 


X s 


Rs 2 + X s 2 ’ 


(78) 


where the conductance G and susceptance B are 
seen to be 


G = 

B = 


R t 


Rs 2 + X* 2 ’ 
X, 


(79) 


Rs 2 + XX 

From equations (68) and (69) it is seen that 


conductor, the impedance Z r becomes a sizable 
fraction of R s . We need expressions for the cor- 
rections that may be needed in interpreting 
such tests. By replacing R s by ( R s + A# s ) and 
X s by ( M s -f- AX S ) in equations (68) and (69), 
we get 

it = r+i„cosa[ MoSin(a +/3) + rriX f “ 2 } 

(82) 

it = . ~ Mo . [ g M « c ° B( «+0 + rtw M 

1 + -Q-sina L 

(83) 

It will be observed that these equations re- 
duce to the differential forms when M 0 is small 
enough. For larger signals the equations indi- 
cate the presence of a “d-c shift” which is small 
when Q is large. They also show that equation 
(76) is in error by a fraction equal to M 0 even 
for very large Q. Thus in tests where M 0 is 10 
per cent the field measurements are accurate to 
10 per cent and can be corrected if desired. 
Some caution must be used in applying equa- 
tions (82) and (83) to an actual case since in- 
duction fields will also contribute to Z r at about 
the same separation that leads to large M 0 . 

However, in most fuze applications M 0 is 
about 0.5 per cent, and the differential forms 
have ample accuracy. 



and 

G = k 


(80) 


II 

Q3 



Therefore 

dG 

dR p 


and 

G 

R P 

(81) 


dB 

dXp 



B 

X p m 


Finite Signals 





It will be observed later in the chapter that 
the actual working signals when the fuze is 
operating normally are so small that the differ- 
ential representation given above is completely 
adequate. However, when tests are made on the 
fuze by measuring its response close to a large 


Specification of Fuze Circuit 
Parameters 

It has been shown that both the resistive and 
reactive components of the antenna are altered 
by the presence of a reflector. To make a work- 
ing fuze it will be necessary to devise a circuit 
which will respond in some manner to the 
change in antenna impedance. Such circuits are 
described in detail in Chapter 3. 

For purposes of further analysis we assume 
that the voltage or current in some part of the 
fuze circuit changes in response to the antenna 
variations and that this change is used to actu- 
ate the fuze. We will call this particular fuze 
parameter V, representing a voltage, although 
it might as well represent a current. In order 
to continue the discussion of the antenna prob- 




36 


THE RADIATION INTERACTION SYSTEM 


lem, we assume that the behavior of the circuit 
is known and that 


V = f (In R s , In X 8 ) = g (In R p , In X p ), (84) 

where for purposes of convenience we express 
the functional relationship in terms of the natu- 
ral logarithm of the impedance components. 
Thus 


(85) 

We define 


o _ ^ c SV 

p d In R p ’ s ~ d In R s ' 

T = dV • T - dV 

p d In X p ’ s ~ d In AY 


( 86 ) 


The quantities S p , T p or their corresponding 
transforms S s , T s describe the behavior of the 
fuze circuit when the antenna impedance varies. 
S s and S p are called the series and parallel re- 
sistance sensitivities respectively and T s , T p are 
called reactance sensitivities in a similar man- 
ner. All four quantities are functions of X 8 , R s 
or X p , R p which make up the free-space input 
impedance Z 0 of the antenna. In Chapter 3 the 
values of these quantities for typical circuits 
will be derived. 

With the aid of the definitions of equation 
(86) we may write 


dV 

dV 

dV 

dV 


r» dR s . rp dX s 

^ Ts X? 

or dR p „ dX p 

u ' 1 p y ’ 

n p p 

T 

M o (Ss cos ^ sin a) , 


(87) 


o[s p sin (a 


T p _ 


688) 


Mo | S p sin (a + 0) + ^ cos (a + /S) J. 


If we make use of the complex notation and 
always consider dV to be the real part of a cor- 
responding complex quantity, we may write 


dV = MS = MoS 0 eX° ~ *>, 


where 

*-(*•- if) 


(89) 


S = ^.Spsin/3 - “cos0^ - j^S p cos0 - ^sin/3^ : 


(90) 


(91) 


tan 7) 


T 2QS P - ^ (1 - Q 2 ) 
QSs = S p (1 - Q 2 ) + 2 T p ' 


(92) 


The appearance of the terms TJQ and T p /Q 
in equations (91) suggests redefinitions of T s 
and T p to include Q. This can be done (see 
Chapter 3), but T s and T p so defined will then 
not have the logarithmic form commonly used 
for S s and S p . We keep the Q to maintain sym- 
metry with the commonly accepted notation. 

Since we are dealing with different mathe- 
matical representations of the same antenna 
the voltage change dV will be the same no mat- 
ter which representation is used. This was im- 
plicit in equation (89). 

The basic equation (89) represents in simple 
form the response of the fuze circuit to a mov- 
ing target. While q is a fixed quantity for any 
given fuze, a (=r —4? tx/\ -f- 8) varies with fuze- 
target separation and therefore with time. The 
voltage change is seen to be proportional to M 0 
and to S 0 , the r-f sensitivity. If the fuze has re- 
actance sensitivity as well as resistance sensi- 
tivity, both contribute to S 0 and give rise to a 
phase shift r\ in the voltage wave dV. By a 
proper selection of antenna coupling, it is often 
possible to operate near a resonance of the 
driving circuit, whereupon T p approaches zero 
and there is little or no phase shift q. 

Inasmuch as dV is proportional to M 0 , a 
space plot of the variation of antenna imped- 
ance will likewise be a space plot of the varia- 
tion of output voltage. This is a most impor- 
tant point to remember. For it means that the 
voltage out of the r-f system can be plotted 
point by point for a slow relative motion of 
fuze and target to give detailed information 
on the performance in rapid motion. All that 
need be changed is the time scale ; the fuze an- 
tenna goes through its sequence of variations in 
whatever time is required for the fuze to move 
through the region of influence, and the wave 
form will be identical in every case. This as- 


ANTENNA IMPEDANCE 


37 


sumes, of course, that the circuit is capable of 
following the time variations, which experi- 
ence has shown is no restriction. 

The space variation of M which gives the 
voltage variation has been called the M wave 
and is so referred to in the discussion which 
follows. Extensive use is made of point-by-point 
plots of the M wave in testing fuzes. 

We note that S may be measured as dictated 
by convenience in terms of either series or 
parallel components, and that the complex form 
of S is completely specified by either set of 
measurements, as shown by equations (89), 
(90), and (91). In many cases T s /QS s and 
T p /QS p are small compared with unity, so that 

Ss = — S p = zSzSq = ±|*S|. 

In any case the basic equation (89) which 
represents the situation is 

dV = MS = M 0 S 0 eK«-'K 

We apply this to the two special cases in which 
we are interested. 

For the ground-approach case we have, uti- 
lizing equation (45a), 

M = Si, G ^ e ^ e ’ a - ( 03 ) 

For the airborne target we have from equa- 
tion (50) # 

M = (cos r)e /a . (94) 

Subscripts previously used in connection with 
A, G, /, 0, and $ will no longer be carried ex- 
cept in cases where there may exist a possibility 
of misunderstanding. 


2 7 ANTENNA IMPEDANCE 0 

The previous section has shown that a knowl- 
edge of the components of Z xu the free-space 
antenna impedance, is essential if circuit re- 
sponse to the reflected impedance arising from 
reflection is to be predicted. This section is con- 
cerned with the values of antenna resistance 
and reactance observed in actual cases. 

c The following bibliographical references are perti- 
nent to this section: 6, 8, 11, 28, 30-34, 37, 38, 49, 50, 52, 
54-60, 62-67, 69. 


Specifically the resistance and reactance sen- 
sitivities of the fuze circuit are functions of 
( X S ,RJ or (X V ,R V ) and must be evaluated at 
the particular operating point characteristic of 
the particular antenna used. Since the various 
missile-antenna combinations present widely 
different impedances, it becomes necessary to 
measure, or in some cases to calculate, the sen- 
sitivity parameters for a given circuit over a 
large range of load impedance, so that the an- 
tenna can be designed to have an operating 
point as near as possible to the optimum point 
for circuit response. It should be pointed out 
here that there are limitations to the antenna 
impedance that can be achieved within the 
limits set by the tactical situation and by speci- 
fied military characteristics. Likewise the val- 
ues of S can be changed by circuit design only, 
within certain limits set by present-day vacuum 
tubes. Thus antenna design must be coordi- 
nated with circuit design to give optimum per- 
formance within the limits of both. In addition 
it is necessary to set up dummy antennas for 
testing fuzes. A knowledge of actual antenna 
impedance is essential here also. In this section 
we are concerned with the antenna impedances 
that can be effectively achieved. Chapter 3 will 
give details about the circuit performance 
under the load and load variations presented 
by the antenna. 


2-71 Specification of Antenna Terminals 

In all the previous discussion the fuze an- 
tenna has been treated as a two-terminal box 
which sends out radiation. No detailed knowl- 
edge of the internal circuit was assumed. We 
imagine this antenna to be connected to a 
circuit whose sensitivity is specified. Now when 
the whole is connected together, a given reflec- 
tor in space sets up a certain A V in the r-f 
circuit. Once the whole arrangement is con- 
nected, the antenna terminals lose their iden- 
tity and their location becomes arbitrary. Thus 
if we open the arrangement at any two points 
(see Figure 9) and call everything on one side 
of the cut the fuze circuit and everything on 
the other side the antenna, the values of X v , R p 
and S p and T }) must be so related that the value 


SECRET 



38 


THE RADIATION INTERACTION SYSTEM 


of AF calculated by their use is independent of 
the particular pair of points selected as an- 
tenna terminals. 

Thus in specifying fuze performance or an- 
tenna performance we are at liberty to select 
any two terminals within the network as an- 
tenna terminals. It has been customary in vari- 
able-time [VT] fuze work to consider all the 
circuit elements inside the fuze electronic as 
the fuze circuit, even if the assembly contained 
some antenna impedance matching network, 
and consider the points where the leads from 
this circuit are connected to the external radi- 



"I 

III 


□ 

TARGET 


Figure 9. Arbitrary division into fuze circuit 
and antenna. 


ating system as the antenna terminals. The dis- 
cussion of the antenna problem has assumed 
that the only ohmic losses in the antenna are 
radiation losses. Experiments have shown this 
to be a valid assumption with the antenna ter- 
minals just specified. If some other pair of 
points is selected so that some energy-absorb- 
ing coupling elements are included in the net- 
work, due account must be taken of these losses. 


2 7 2 Experimental Measurement of R P 

The parallel radiation resistance R p is meas- 
ured by a substitution method. A typical fuze 
circuit is used as an indicator. In the fuze 
circuit several quantities, such as diode voltage 
V d or oscillator grid voltage E g , oscillator plate 
current I p , and carrier frequency /, are all func- 
tions of (X p ,R p ). The fuze is first placed on the 
projectile on a high stand and the free-space 
values V d or E g , I p , and / noted. The fuze is 
then removed from the projectile and placed in 
a shield box. Reactance and resistance are 
added to the antenna terminals until the free- 
space values are duplicated. It is assumed that 
the shield box does not load the fuze at all, so 
that the amount of resistance across the ter- 


minals when the load is duplicated repre- 
sents R p . 

In making this measurement the exciting cap 
or bars are often not removed. The resistors 
are merely substituted across the points that 
have been previously agreed upon as the an- 
tenna terminals. The shield adds reactance to 
the antenna so that direct measurements of X p 
are not obtained this way. 

To show that the shield does not introduce 
serious losses, the whole antenna is removed 
from the fuze and resistors substituted directly 
across the fuze terminals. The size of the ar- 
rangement is so small compared to X that radia- 
tion is negligible and the substituted resistance 
represents R p . By such tests it has been shown 
that shield losses are negligible, so that the 
more convenient shield box can be used where 
desired. In making this comparison test it is 
necessary to remove dielectric insulators so 
that losses in them do not confuse the measure- 
ments. 

In the case of fuzes which use the projectile 
as the antenna, the radiation load is removed 
by putting a shield can over the nose fuze, as 
shown in Figure 10. Such an arrangement re- 
places radiating currents in the antenna by 
nonradiating currents inside the shield can and 
thus substitutes can losses for antenna losses 
in measuring R p . If both are small compared 
with the true radiation losses, this substitution 
causes negligible error. The final proof that the 
errors are negligible is obtained by making a 
pole test (see Section 2.12) and comparing 
actual signal with calculated signal based upon 



SHIELD BOX 

Figure 10. Method of removing radiation load 
without removing projectile. 


the measured values of R p and S p . Within an ex- 
perimental error of less than 10 per cent there 
is agreement. 

It is interesting to note here that the absolute 
ohmic value of the substitution resistors used 
for the measurement of R p need not be known. 


SECRET 



ANTENNA IMPEDANCE 


39 


Since M is proportional to dR p /R p , only ratios 
of resistances are needed, and any set of resis- 
tors whose r-f resistance is a constant fraction 
of the d-c resistance may be used. It has been 
found that International Resistance Company 
[IRC] type F-l or F-% resistors fulfill this 
requirement; in fact their r-f values are quite 
close to their d-c values. However, if it is of 
importance to know the power radiated, as 
is the case in jamming calculations, the true 
value of the r-f resistance must be known. It 
has been customary for all collaborating lab- 
oratories to use equivalent sets of r-f resistors 
supplied by a central laboratory. 


2 7-3 Specification of X p 

The quantity T p /QS p appearing in equation 
(91) is in many cases so small that it can be 
neglected, as has already been mentioned. To 
see this, the value of T P /QS P at the operating 
point must be evaluated, a procedure which re- 
quires knowledge of X p . The question immedi- 
ately arises: Is the total apparent reactance 
across the antenna terminals the correct value 
of X p , or should we use only the part that 
appears by virtue of radiation? The argument 
above about specification of antenna terminals 
implies that either arrangement should give 
the same answer. The r-f section of the fuze 
can be represented in block diagram as in Fig- 
ure 9. The target in space gives rise to a cer- 
tain XV out of the terminals to the audio-con- 
trol circuit. We are at liberty to divide the 
whole arrangement at any convenient place by 
a line xx and call the left part the fuze and 
the right part the antenna. If the calculations 
are performed properly, the result must be the 
same no matter where xx is chosen. We choose 
to put the fixed part of the antenna reactance 
to the right of xx and call it a part of the an- 
tenna. Similarly, if there are dielectric losses 
in the antenna mounting, we can assume them 
to be represented as a resistance across the 
antenna terminals and put it to the left of xx 
as a part of the fuze circuit. This is the adopted 
convention. As a matter of fact we can, if we 
desire, divide the X p any way we choose be- 
tween fuze circuit and antenna. 


To illustrate the point we show that the quan- 
tity T p /Q is independent of how X p is defined 


Suppose 



dV 

dX p ’ 


(95) 


This does not 
Then 


X, 


2 xfC 9 

affect the generality of the result. 


dV = dV dC p 
dX p dC p dX p 

and 

Tp = XI dV_ = -1 

Q R p dXp fRp dC p 


(96) 

(97) 


which shows that T p /Q is independent of how 
C p is defined. 


2 7,4 Measurement of X p 

In the following discussion X p is considered 
as the total reactance across the antenna ter- 
minals. The term X p is measured by a direct 
substitution method. The fuze is mounted on a 
missile, and values of V d or E g , I p , and / are 
recorded. The fuze is then removed from the 
vehicle and the circuit disconnected from the 
antenna at the previously selected terminals. 
Resistors and condensers are placed across the 
terminals until V d , I p , E g , and / are duplicated, 
thus duplicating R p and X p . For all fuze designs 
now used X p is capacitative. To a good approxi- 
mation X p is the capacity across the antenna 
terminals as measured by low-frequency meth- 
ods. This is shown by the fact that X p varies 
only slightly with projectile size. 31 


2.7.5 Effect of Feed Geometry 

upon R p and X p 

Figure 11 shows the effect upon R p of chang- 
ing the size of the exciting ring on the T-50 
type of fuze, with the spacing from ring to 
ground held constant at 1 in. Results are shown 
for several bombs, two carrier frequencies 
(White and Brown) for ring lengths ranging 



40 


THE RADIATION INTERACTION SYSTEM 


from 14 to 3 in. As expected, an increase in 
ring length decreases R p . 

The effect of ring length upon C p is shown in 
Figures 12 and 13 for Brown and White fre- 



Figure 11. R p as function of ring size; BRLG- 
type fuze; gap width, 1 in.; solid lines, Brown 
frequency; broken lines, White frequency; curves 
1, M-30 100-lb bomb; curves 3, M-64 500-lb bomb; 
curves 4, M-65 1,000-lb bomb; curves 5, M-66 
2,000-lb bomb; curves 6, M-81 260-lb bomb. 

quencies respectively, with a constant gap size 
of 1 in. In Figures 12 and 13 the capacity is 
shown as 6.9 ppf for all the bombs, for a ring 
length of 1 in. This is not precisely correct, as 
capacities associated with the various projec- 
tiles vary somewhat; the curves are meant to 
indicate the variation of the capacity with ring 
size. The value 6.9 ppf is not far from correct, 
however; for all the bombs, the true range of 
values at the 1-in. point is about 6.9 ± 0.5 qpf. 
An increase in ring length increases C p . 

The effect of gap size upon R p and C v is 
shown in Figure 14. The size of the gap in the 
range shown (spacings from 1/2 to 1 in.) has 


virtually no effect upon R p . The term C p , of 
course, decreases as the spacing is increased. 
It thus becomes possible, within the limitations 
of space requirements, to vary the gap size to 
bring C p to a favorable value without affect- 
ing R p . 

In the case of transverse center-fed dipoles 
(T-51, T-82) C p is increased by increasing the 
size of the dipoles or by reducing their separa- 
tion. The term R p decreases when the size of 
the dipole is increased While it is an 

advantage to get lower R p by using longer 
dipoles, air resistance and operational difficul- 



1/4 1/21 2 3 

RING SIZE (INCHES) 


Figure 12. C P as function of ring size; BRLG- 
type fuze; gap width, 1-in.; Brown frequency; 
curve 1, M-30 100-lb bomb; curve 3, M-64 500-lb 
bomb; curve 4, M-65 1,000-lb bomb; curve 5, 
M-66 2,000-lb bomb; curve 6, M-81 260-lb bomb. 


ties increase with increasing length, and these 
considerations serve to limit the length of an- 
tenna which may be used. Electric efficiency 
must be subordinated in this design. 


SECRET 



ANTENNA IMPEDANCE 


41 


Typical Values of R p and X p 

Figure 15 shows the value of R p as a function 
of carrier frequency for several common bombs 
using a standard T-50 ring; the feed must be 
specified since R p depends on it. The large 
range of values for all bombs at any one fre- 



RING SIZE (INCHES) 


Figure 13. C P as function of ring size; BRLG- 
type fuze; gap width, 1 in.; White frequency; 
curve 1, M-30 100-lb bomb; curve 3, M-64 500- 
lb bomb; curve 4, M-65 1,000-lb bomb; curve 5, 
M-66 2,000-lb bomb; curve 6, M-81 260-lb bomb. 

quency illustrates clearly the difficulty of de- 
signing a single fuze which will work on all 
bombs. It was for this reason among others 
that the T-51 type transverse antenna fuze was 
designed. The T-51 with its independent an- 
tenna has radiation resistance relatively inde- 
pendent of projectile size. 

The logarithmic spread in R p among the 
vehicles tends to decrease as the frequency is 
lowered, The mean value of R p increases. Until 
recently, as shown in the next chapter, it was 



1/2 5/8 3/4 7/8 I 


S PACING - RING TO BASE OF CAP (INCHES) 

Figure 14. Effect of gap size upon R P and C P ; 
BRLG-type fuze; M-65 1,000-lb bomb; White 
frequency. 

not feasible to operate fuze circuits into a mean 
value of R p as high as 40,000 ohms. The im- 
proved reaction grid detector [RGD] circuit 



B-35 BH5 B+5 W-IO W+IO W+30 


FREQUENCY 

Figure 15. R P as function of carrier frequency; 
T-50 ring; curve 1, M-30 100-lb bomb; curve 2, 
M-57 250-lb bomb; curve 3, M-64 500-lb bomb; 
curve 4, M-65 1,000-lb bomb; curve 5, M-66 2,000- 
lb bomb; curve 6, M-81 260-lb bomb. 


(SWHOI 




42 


THE RADIATION INTERACTION SYSTEM 


5" HVAR 



Figure 16. Scale outline drawings of a number of missiles for which VT fuzes were designed. Fuzes 
with longitudinal excitation were designed for all missiles shown. Transverse antenna fuzes were also 
designed for bombs. To show the relative size of fuze and missile, the outline of the fuze is shaded. 


SECRET 


DIRECTIVITY PATTERNS 


43 


described in Section 3.1 makes it possible to 
use one frequency for a large number of projec- 
tiles by allowing operation at a high value 
of R p . 

Complete tables of R p and X p are not avail- 
able for all projectiles. Table 1 gives the values 
at important frequencies for fuze projectile 
combinations of current interest. The range of 
missile sizes for which fuzes were designed is 
illustrated in Figure 16. Photographs of typical 
fuze and missile combinations are shown in 
Figure 7 of Chapter 1. 


Table 1. Typical values of R p and X p for various 
fuze-projectile combinations. 


Fuze 

type 

Projectile 

Carrier 

frequency 

R P 

(ohms, 

ap- 

prox.) 

(ohms, 

ap- 

prox.) 

T-91 

M-30 bomb 
(100-lb GP) 

Brown 

20,000 

300 

T-91 

M-66 bomb 
(2,000-lb GP) 

Brown 

40,000 

300 

T-92 

M-64 bomb 
(500-lb GP) 

White 

11,000 

200 

T-92 

M-65 bomb 
(1,000-lb GP) 

White 

10,000 

200 

T-132 

M-43 mortar 
with M-56 tail 

White + 20 

20,000 

150 

T-132 

M-56 mortar 

White + 20 

6,000 

150 

T-171 

M-43 mortar 
with M-56 tail 

Brown 

90,000 

300 

T-171 

M-56 mortar 

Brown 

60,000 

150 

M-166 


White + 35 

150,000 

600 

T-2005 

HVAR rocket 

Brown 

3,800 

150 


AR 5-in. rocket 

Brown 

3,600 

150 

T-5, T-6 

M-8,4|-in. 

rocket 

White + 30 

8,000 

300 


28 DIRECTIVITY PATTERNS d 

We come now to a more detailed study of the 
properties of / 2 (0,<£), the power radiation 
pattern or directivity pattern. The importance 
of / 2 (0,0 ) was indicated in Section 2.5 above, 
where it was shown that the reflected impedance 
Z r , due to an object situated in a direction 
( 0 i 3 ><£i 3 ) relative to the fuze, is proportional to 
fi ( 013 , 013 ). Furthermore, the gain G is a func- 
tion of 

d Bibliographical references pertinent to this section 
are 6, 8, 36, 40, 47, 50, 52, 54-60, 62, 63, 64, 68. 


281 Measurement of Directivity Patterns 
Experimental Setup 

The simple convenient method which has 
been devised for the measurement of directivity 
patterns may be understood with the help of 
the photographs in Figures 17, 18, and 19. In 
Figure 17 the antenna, which consists in this 
case of the projectile plus the fuze in its nose, 
is mounted horizontally on a platform about 
15 ft above the ground. The platform is free 
to rotate about a vertical axis (Figures 18 and 
19). The receiver (Figure 17), consisting of a 
dipole antenna feeding a detector, is situated 
about 150 ft from the transmitter. Power is fed 
to the transmitting antenna by means of a care- 
fully choked line coming from the power supply 
on the ground. The line is attached to the an- 
tenna at a voltage node. The whole setup is 
situated in an open field. The radiating antenna 
can be rotated through any angle and the re- 
ceiver signal plotted as a function of this angle. 
The plate supply of the transmitting oscillator 
is based upon an a-c source of 60 c. Full-wave 
rectification with no filtering is used; there is 
thus a plate modulation frequency of 120 c 
which can be detected at the receiver. 

In the type of fuze antenna shown in the 
photograph, the directivity pattern has cylin- 
drical symmetry because of the symmetry of 
the projectile. In such a case the directivity has 
no dependence upon 0, and the pattern may be 
represented analytically as / 2 (0). The angle 
of rotation about a vertical axis is then equal to 
6 ; when the nose points directly at the receiver 
^ = 0°. The detector used is of the square law 
variety, so that the audio signal is directly pro- 
portional to the square of the field strength or 
to f 2 (0). 

Where cylindrical symmetry is not present, 
the pattern must be taken in several planes to 
get a reasonably complete set of values for 
f 2 (0,0) . Such asymmetry may occur when the 
antenna is separate from the bomb, as in the 
T-51 and T-82 type designs, the bomb acting as 
a parasitic reflector or director. 

Detector Circuit 

Some notes may be added concerning the de- 


SECRET 


:ET| 


44 


THE RADIATION INTERACTION SYSTEM 


tector circuit, shown in Figure 20. The circuit 
and physical layout are symmetrical, with a 
view to obtaining balance with respect to 
ground. This has the effect of minimizing the 
effect of any vertically polarized components of 
the field caused by reflection from the ground, 
which otherwise could alter the apparent shape 



Figure 17. Field setup for obtaining directivity 
patterns. 


of the directivity pattern, especially affecting 
the symmetry of the patterns. 

The r-f chokes are for the purpose of reduc- 
ing interference from transmitters operating 
in or around the broadcast region. These chokes 
have a high impedance at the carrier frequen- 
cies used in fuze antennas but a low impedance 
at lower frequencies. The coupling condensers 


vacuum-tube voltmeter, preceded if necessary 
by an amplifier. 

The output of the detector follows quite accu- 
rately a square law for outputs up to 100 mv. 



Figure 19. Platform of Figure 18 shown 
lowered to ground. 


The output may be kept below this level by 
adjusting the power supply feeding the trans- 
mitting antenna. 



Figure 18. Rotatable platform holding fuzed 
bomb for directivity pattern measurements. 


Reflections from Ground 

The reflections from the ground contribute 
to the output of the detector and therefore may 



in the grid circuits prevent the grids from 
being shorted by the chokes at direct current. 
The condenser from the plates to ground serves 
as an r-f by-pass; it has a high impedance to 
audio frequencies. 

The audio output is fed to a Ballantine-type 


Figure 20. Detector circuit; components are 
enclosed in metal box mounted between arms of 
receiving dipole. 

change the apparent directivity pattern. This 
matter has been studied and is presented in 
some detail as supplementary material in Sec- 


DIRECTIVITY PATTERNS 


45 


tion 2.15, where it is shown that the ground 
reflection introduces negligible error for the 
simple radiation patterns now used. 

By means of the equipment described above 
a large number of directivity patterns have 
been obtained. The patterns fall into two 
classes: (1) patterns for fuzes which use the 
projectile as the antenna (longitudinal excita- 
tion), and (2) patterns for fuzes which use a 
separate antenna such as a short transverse 



Figure 21. Directivity pattern for M-64 bomb 
at B — 16; longitudinal excitation; G = 1.55. 


dipole or loop (transverse excitation). The pat- 
terns will be discussed according to this classi- 
fication. 

Longitudinal Excitation 
Typical Patterns 

In longitudinal excitation the fuze proper is 
connected to the projectile at one end. The an- 
tenna, consisting of fuze and projectile, is split 
by an insulator near the end for the purpose 
of feeding energy to it. The exact position and 
size of the gap over the range used, while im- 
portant in determining the antenna impedance, 
have little effect upon the pattern. Therefore it 
will not be necessary to specify the feed exactly 


in describing the patterns for longitudinal ex- 
citation. 

A preliminary idea of the character of the 
patterns may be obtained from Figures 21, 22, 
and 23. These show the directivity patterns 
f 2 (6) plotted versus 0 on polar coordinate 
paper; for these antennas, the directivity pat- 
tern is not a function of <£, cylindrical symme- 
try being present. Figures 21, 22, and 23, for 
a 500-lb GP bomb (M-64) at three carrier fre- 



Figure 22. Directivity pattern for M-64 bomb 
at B -f- 15; longitudinal excitation; G = 1.9. 


quencies, demonstrate the effect of changing 
the frequency. As the carrier frequency is 
raised, which means the antenna becomes elec- 
trically longer, the pattern departs more and 
more from the simple sin 6 pattern of an ele- 
mentary dipole (shown in Figure 24). The 
minor lobes in the pattern for a carrier fre- 
quency of W + 10 (see Figure 23), will be 
noted. In these patterns, as in all the patterns 
obtained with longitudinal excitation, the radi- 
ation is more intense off the end of the antenna 
away from the feed point. This will be dis- 
cussed below in greater detail. The values of G 
for each pattern are given in the captions to the 
figures. These values were obtained by graphi- 
cal integration of the patterns. The effect of 
using one frequency for exciting various pro- 


46 


THE RADIATION INTERACTION SYSTEM 


jectiles is shown in Figure 25. Figure 25 repre- 
sents a series of patterns at W + 10 for the 
M-30, M-81, M-64, M-65, and M-66 bombs. In 
this figure the patterns are plotted in rectangu- 
lar coordinates. 

Since tactical utility has required that the 
fuze be located in the nose of the projectile, we 
are interested in the values of f 2 (0,<f>) in front 
of the equatorial plane, i.e., for 6 < 90 degrees 
in the patterns of Figure 25. It is immediately 



Figure 23. Directivity pattern for M-64 bomb 
at W + 10; longitudinal excitation; G = 2.6. 


may be expected from qualitative arguments. 
The antenna may be thought of, crudely, as a 
piece of transmission line with a generator at 
one end and an impedance at the other end. A 
wave starts out from the generator ; some of it 
is absorbed in the impedance at the other end 
(radiation) ; the rest is reflected back. Since 
the amplitude of the wave traveling from the 
generator is greater than that of the return 
wave, the part of the radiation due to the for- 



Figure 24. Directivity pattern for infinitesimal 
dipole; / 2 (0) = sin 2 (0) ; G — 1.5. 


evident that there is a wide range in Z r for 
targets in the range 10 to 90 degrees off the 
nose. This is a complicating factor which re- 
quires that more than one frequency be used 
in designing longitudinal antenna fuzes. 

This is an unfortunate complication that 
could largely be avoided if the feedpoint could 
be located in the rear of the projectile. 

General Features of Longitudinal 
Patterns 

The directivity patterns obtained with longi- 
tudinal excitation have several general fea- 
tures worthy of note. Some of these have 
already been mentioned and will be treated 
here in somewhat more detail. 

“Lean” of Patterns. The patterns “lean” 
away from the feedpoint. This characteristic 


ward wave, primarily forward radiation, is 
more dominant than the part due to the return 
wave. 

For end-fed antennas, at a given frequency, 
the asymmetry is greater the greater the thick- 
ness of the antenna relative to its length. Cen- 
ter-fed antennas, even if of considerable thick- 
ness, have symmetrical patterns. 

Patterns like those experimentally obtained 
may be computed by assuming an antenna cur- 
rent distribution with features as above de- 
scribed. That is, suppose we assume that the 
antenna current I is given by an expression of 
the form : 

/ = e jUt - z) _ RI ie -j(2n/\)(L - z) 

(98) 

In equation (98), h represents the amplitude 


SECRET 


DIRECTIVITY PATTERNS 


47 


of a wave traveling in the positive z direction, 
z is the running coordinate of the antenna with 
the feedpoint at the end z = 0, L is the length 
of the antenna, and RI X represents the ampli- 
tude of a return wave. Thus R is a reflection 
coefficient whose magnitude is less than unity, 
and 5 represents a phase shift occurring at re- 
flection. Thus 1 represents a return wave super- 
posed upon a forward wave. 

Now the angular dependence E (6) of the 









//} 

1 


- 


'il 

1 



f ¥ 

' H 

\ III 

« 




- 1 
// 

i 

# \ 

\ HI 

v// 

m 

¥ 

. 0 

/ • A 1 

/\ 

1 ^ 

\T 

./ .j— 

a n 1 AA 1 

1 

or\ IAA u 

in ion 


e (DEGREES) 


Figure 25. Directivity patterns at W + 10; 
longitudinal excitation; curve 1, M-30 100-lb 
bomb; curve 3, M-64 500-lb bomb; curve 4, M-64 
1,000-lb bomb; curve 5, M-66 2,000-lb bomb; 
curve 6, M-81 260-lb bomb. 

remote radiation field produced by a linear an- 
tenna of length L is given by 

L 

E(e) a sin 9 J I(z)e l * cos e\ y Z} (99) 

0 

where I (z) is the current distribution along z. 

It has been found that if I (z) be taken as in 
equation (98), then normalized values of E 2 (6) 
obtained from equation (99) agree well with 
experimentally obtained patterns when R and 5 
are adjusted empirically. The picture of a for- 
ward wave and a return wave appears to be 
adequately correct to allow extrapolation and 
interpolation for changes in antenna size. 


Small-Angle Radiation. Experimental meas- 
urement of patterns and the theoretical compu- 
tations of patterns outlined above (see Section 
2.10) both lead to the conclusion that, for small 
angles, we may express the directivity pattern 
as 

P(6) = a sin 2 d, (100) 

where a is a different constant for each projec- 
tile. This is a valuable generalization that facil- 
itates computation of Z r for cases arising in 
practice. 

Effect of Projectile Geometry. Because of the 
considerable thickness of the projectile anten- 
nas, their physical lengths are considerably less 
than their “electrical” lengths. For a given 
physical length, an increase in thickness serves 
to increase the electrical length. 

Effect of Tuning or Loading. The pattern de- 
pends only upon the frequency and the antenna 
geometry. There is, of course, no effect due to 
tuning or loading the antenna circuit. 

Comparison of Patterns for Fuze Work 

One of the desiderata of a proximity fuze is 
that it be usable without modification on vari- 
ous projectiles. It thus becomes necessary to 
examine, among other things, the variations in 
the directivity patterns for the various projec- 
tiles. This variation, for longitudinal excitation, 
has already been illustrated in Figure 25, where 
it is shown that at a particular frequency the 
patterns vary considerably. In the search for 
an optimum operating frequency for a prox- 
imity fuze for bombs, a large number of direc- 
tivity patterns was taken at various frequencies 
for the several bombs and a comparison of 
f 2 (0) was made. In this comparison, relatively 
small values of 0 are of importance in the 
ground-approach application since it is these 
that are encountered under terminal conditions 
for ordinary bomb releases. Because of the ap- 
proximate law f 2 {6) — a sin 2 6, relative values 
for the various projectiles at one angle, i.e., 
0 =: 30 degrees, will hold, roughly, for smaller 
angles. Figure 26 presents the values of 


for various bombs for a range of frequencies. 
From Figure 26 it is seen that the expected 


SECRET \ 


48 


THE RADIATION INTERACTION SYSTEM 


variation in signal covers a very wide range, 
except at frequencies of 50 me and below. This 
agrees with the discussion in Section 2.5.6, 
which indicated that the signals for various 
bombs tend to approach the same level as the 
electrical length of the antenna is shortened 
below 1/2. Until close to the end of World 
War II it was not feasible to use frequencies 
as low as 50 me, because the values of parallel 
radiation resistance encountered at these low 
frequencies (see Figure 15) would not permit 
efficient matching to the driving circuit, thus 



Figure 26. Relative signal strength Mo/h = 
(X/47 r) Gp(e) at 6 = 30°, over a range of fre- 
quencies; longitudinal excitation; curve 1, M-30 
100-lb bomb; curve 2, M-57 250-lb bomb; curve 
3, M-64 500-lb bomb; curve 4, M-65 1,000-lb 
bomb; curve 5, M-66 2,000-lb bomb. 


leading to low S values for high R p . If the re- 
flected signal is to be nearly the same at all 
heights for different projectiles using the same 
fuze, the product S 0 M 0 must be constant. The 
term M 0 depends upon the directivity pattern 
and So depends upon the operating point R p . 
To hold the spread of S 0 M 0 to reasonable values, 
it was found necessary to use two different 
radio frequencies in order to accommodate the 
fuze to various bomb sizes. It will be seen in 
Section 2.8.4. that transverse excitation largely 
avoids this difficulty. Toward the end of World 
War II a circuit was developed which could be 
matched to the high values of parallel radiation 


resistance encountered at low carrier frequen- 
cies. This made possible the design of a more 
nearly universal longitudinal excitation fuze for 
bombs. 40 


Transverse Excitation 
Transverse Dipole 

Fuzes working on this principle use a short 
transverse dipole as an antenna. The body of 
the projectile is not intentionally used as a part 
of the fuze, although it introduces complica- 
tions as shown in Section 2.5.4. Space limita- 
tions are such that the transverse dipole is 
short compared to a half wave, and the direc- 
tivity pattern tends to be like that for a short 
thin wire antenna, f 2 {6) — sin 2 6 (see Figure 
24). The close presence of the body of the pro- 
jectile modifies the pattern so that it is no 
longer a figure of revolution about the antenna 
axis. In some cases the projectile acts like a 
director, making the radiation toward the back 
of the projectile greater than toward the front. 
A certain amount of asymmetry with respect 
to the bomb axis is sometimes present because 
of a slight unbalance in the feed. 

An unbalanced feed for the transverse dipole, 
aside from the effects discussed in Section 
2.5.4, gives rise to a directivity pattern which 
does not have axial symmetry. In Section 2.5.4 
it was seen that the longitudinal currents give 
rise to a correction which is small if the longi- 
tudinal currents are kept small. 

To verify the fact that these currents are 
small the radiation pattern of the fuze-projec- 
tile combination is measured with equipment 
arranged similarly to that shown in Figure 17. 
The projectile axis is horizontal and the axis 
of the transverse dipole is vertical. The re- 
ceiver, which is sensitive only to horizontally 
polarized radiation, does not receive the energy 
radiated by the transverse currents flowing in 
the fuze dipole and the projectile behind it. It 
receives only the radiation from the longitudi- 
nal currents and gives a pattern like those for 
axial feed (see Figures 21, 22, 23, and 25). 

The strength of the axial radiation is com- 
pared with the strength of the dipole radiation 
by putting the fuze dipole in the horizontal posi- 
tion and pointing the projectile directly toward 


SECRET 


DIRECTIVITY PATTERNS 


49 


or away from the receiver. In this orientation 
the longitudinal currents do not radiate toward 
the receiver, and the received signal is that 
from the transverse dipole alone, modified by 
the reflecting properties of the projectile. As a 
result of the two measurements, two field in- 
tensities are obtained which show the relative 
amounts of energy radiated by the longitudinal 
and transverse currents. In order to suppress 
the longitudinal currents it has been found 
necessary to use a relatively long wavelength 
so that the projectile is nonresonant. 

When the directivity pattern is measured with 
fuze dipole horizontal and projectile horizontal, 
an asymmetric pattern like that in Figures 27 



Figure 27. Directivity pattern for M-57 bomb 
at W -(- 35; transverse excitation; pattern taken 
in plane determined by longitudinal axes of dipole 
and bomb. 

and 28 is obtained. The right-left asymmetry 
arises from the addition of the patterns from 
longitudinal and transverse currents. The fore- 
aft asymmetry arises from the reflecting prop- 
erties of the projectile. For short projectiles 
(see Figure 27) the fore-aft asymmetry is less 
marked than for larger ones. 

As we have seen, if the longitudinal current 
is small its effects can be neglected. Thus, to a 
good working approximation, we can take the 
directivity in the directly forward direction to 
be unity and the directivity in other directions 


forward of the equatorial plane as cos 2 a or 
sin 2 6 . 

When the transverse dipole is used, the size 
of the projectile has but little effect on the radia- 
tion resistance, provided the diameter is not too 



Figure 28. Directivity pattern for M-64 bomb 
at W + 35; transverse excitation; pattern taken 
in plane determined by longitudinal axes of 
dipole and bomb. 

large and the projectile does not form an effec- 
tive shield by imaging the dipole. This type of 
antenna is effective on all types of American 
bombs which the fuze will fit. It is not satisfac- 
tory with the British-type square-nosed bombs 
like the 4,000-lb LC, since this kind of bomb 
forms an effective shield unless the fuze is 
mounted on an extension. The British have 
found by extensive tests that a short extension 
makes the fuze quite satisfactory on this bomb. 

Furthermore, the vehicle has only a relatively 
minor effect on the pattern, as we have seen, so 
that the fuze operation becomes relatively inde- 
pendent of the size of the projectile. In addi- 
tion, the transverse type of excitation will op- 
erate with nonconducting projectiles, such as 
the plywood belly tanks arranged with bomb 
fins used as fire bombs. 

Loop Excitation 

It is possible to obtain transverse excitation 
by means of a transverse magnetic dipole. This 


50 


THE RADIATION INTERACTION SYSTEM 


is achieved by means of a small loop antenna, 
about 3 in. in diameter, whose plane includes 
the axis of the projectile, as in the T-172 fuze. 
The polarization of the radiation is different 
from that of an electric dipole, as shown by 
Table 2. 


Table 2. Polarization of radiation in loop and dipole fuzes. 



Dipole 

Loop 

E r 

0 

0 

E a 

A 

— cos a cos 5 

A . 9 
— sin 5 


r 

r 


A . 

A 

Ed 

— sin 5 

— cos a cos 5 


r 

r 


The coordinate system for Table 2 is as de- 
fined in Section 2.5.4. Aside from the polariza- 
tion change the argument is similar to that 
outlined for the transverse dipole, including 
unbalance effects. Similar radiation measure- 
ments are required, with due consideration for 
the polarization. 

29 WORKING SIGNALS; 

GROUND-APPROACH CASE e 

This chapter is primarily concerned with the 
variations of antenna impedance as the fuze 
approaches a reflecting target. This variation 
has been described by M, and the variation of M 
from point to point in space has been called the 
M wave. It has also been shown that the voltage 
change dV out of the r-f system can be specified 
in terms of circuit parameters. 

dV = MS. (89) 

In other words, the voltage out of the r-f system 
is proportional to M, and in so far as relative 
wave form and amplitude are concerned M can 
be considered as a working signal set up by the 
reflecting target. Chapter 3 deals with the prop- 
erties of circuits and the values of S that can 
be achieved. 

The method of utilization of this signal has 
been indicated in Chapter 1 and will be briefly 
recapitulated here. The voltage dV is applied 
to an amplifier; the output of the amplifier is 
applied to the grid of a thyratron; when the 


output of the amplifier is of the proper magni- 
tude and phase the thyratron discharges 
through a detonator which initiates the firing 
train resulting in the burst. In most cases the 
transmission time of the signal through the 
fuze and detonator are negligible. A treatment 
of the delay to be expected is given in Chapter 
3, which deals with the audio amplifier and 
firing circuit. Since delays are generally small, 
the basic problem of the design is to make the 
output voltage of the amplifier reach the firing 
level at the moment when the projectile is in a 
position such that its burst would do the maxi- 
mum amount of damage. While the necessary 
adjustments could be made empirically upon 
the basis of field trials, it is extremely helpful 
to be able to predict the expected point of func- 
tion from the fuze parameters and the ballistic 
problem. Such a knowledge allows treatment 
of many cases based upon performance in a 
typical case; it also aids recognition of abnor- 
mal performance. 

We proceed to show how the prediction is 
made for the case of a bomb approaching the 
ground. For the sake of clarity we first treat a 
special case in Section 2.9.1 and then turn to 
a discussion of each of the factors involved in 
Section 2.9.2. 

2 91 Prediction of Height of Function 

The case selected is that of the ring-type fuze 
(longitudinal excitation and White frequency 
band) on the M-64 (500-lb) bomb, released 
from level flight by an airplane flying at 200 
mph from an altitude of 10,000 ft over earth 
which has a reflection coefficient of 0.5. 

The equation governing this case, equation 
(93), has been derived in Section 2.6.2. Utiliz- 
ing it, we have 

dV = MS = G/ 2 (0,0)e y[( - 4 ' vx) + J 

( 101 ) 

Equation (102) represents an audio-frequency 
voltage with peak amplitude 

MoS 0 = ( 102 ) 

and frequency 


dh 

2 

dh 

dt 

." * 

dt 


e Bibliographical references pertinent to this section 
are 12, 16-22, 27, 35, 39, 40, 70, 71, 74. 


SECRET 


WORKING SIGNALS; GROUND-APPROACH CASE 


51 


For a falling bomb dh/dt is essentially con- 
stant over the last few hundred feet of flight, 
and we can take dh/ dt as the vertical component 
of the striking velocity. Thus equation (101) 
represents a voltage of constant frequency and 
rising amplitude in the range in which there 
is appreciable reflected signal. 

Let us assume that the steady-state voltage 
amplification of the amplifier is known in the 
form of a curve g(F), henceforth denoted sim- 
ply by g and that the net holding bias of the 
firing thyratron is B. Then we can say that the 
height of burst h is approximately 

h = XnSo £ r-(e,<t>) (104) 

Equation (104) is based upon the tacit as- 
sumption that there is no delay in the amplifier 
and detonator, and further it ignores the fact 
that the thyratron can only fire when the volt- 
age is positive, thereby introducing an uncer- 
tainty in the height of operation of approxi- 
mately (X/ 2). The nature of these corrections 
will be discussed in more detail in Section 2.9.2. 

The quantity B/g represents the peak voltage 
into the audio-control circuit that is necessary 
to fire the detonator. 

We now insert appropriate values in equation 
(104) for our special case as follows: G/4 jc = 

0.208, the vertical component of striking veloc- 
ity = 740 fps, and the striking angle = 18.5 de- 
grees, the wavelength = 8.2 ft, and / 2 (18.5 de- 
grees) = 0.085. The audio frequency F is 
(2 X 740) /8.2 = 180 c. Typical values of G, B , 
and So, are 80, 4.4, and 15, respectively. Using 
these values, equation (104) gives h — 20 ft. 

This is the height of burst to be expected if 
only radiation fields are involved. Actually the 
induction field introduces a correction, as shown 
in Section 2.10, when the magnitude of h ap- 
proaches X. 


2,9,2 Factors Affecting Magnitude and 
Frequency of Impedance Signal M 

Having taken a brief overall view of the vari- 
ous factors determining the point of function 
of a fuze by computing the position of the burst 
in a typical case, we shall now discuss in more 


detail the various factors affecting the im- 
pedance signal M. We use the term “signal” 
advisedly, because the impedance change is de- 
pendent upon the interaction between fuze an- 
tenna and target, and therefore contains intelli- 
gence as to the conditions of such interaction. 

The amplitude and frequency of the imped- 
ance signal or M wave depend upon a variety 
of conditions, some of which depend upon the 
fuze design and the projectile on which the 
fuze is used, others depending on ballistics and 
reflecting properties of the target. We shall 
omit factors depending upon the circuit adjust- 
ment, which is the subject of the next chapter. 
Aside from these the factors affecting M may 
be grouped according to the following scheme. 

Fuze antenna factors 

1. Directivity pattern. 

2. Antenna gain. 

3. Carrier frequency. 

Ballistic and target factors 

1. Distance from target. 

2. Orientation of fuze antenna relative to 
target. 

3. Speed of approach to target. 

4. Reflecting properties of target. 

We shall discuss each of these factors in turn. 

Fuze Antenna Factors 

Directivity Pattern. It has been shown, equa- 
tion (93), that M is proportional to f 2 (6,(f>); 
the values of 6 and </> in question are those ob- 
tained by drawing a straight line from the an- 
tenna perpendicular to the ground. 

The nature of the patterns in use has been 
discussed in Section 2.8, where there was also 
presented a series of typical patterns. Upon 
referring to these patterns, it is evident that 
in the case of longitudinal excitation f 2 (0) is 
relatively small when the projectile is vertical 
or nearly vertical to ground, and becomes larger 
as the projectile becomes more nearly parallel 
to the ground. 

In the case of transverse excitation, on the 
other hand, / 2 (0,<£) is large when the projectile 
is normal to the target surface. When the angle 
between the surface and the axis of the 
projectile is any value other than 90 degrees, 


■ 


^SECRET 



52 


THE RADIATION INTERACTION SYSTEM 


there is an uncertainty in the value of 
due to the uncertainty in orientation of the 
dipole antenna, as discussed in Section 2.5.4. 
If the angle between the axis of the projectile 
and the normal to the ground (angle of in- 
cidence) is a, then 0 may be any value in the 
range (90-a) degrees to 90 degrees. 

For most applications, the angle of incidence 
a is less than 45 degrees. This means that the 
terminal values of / 2 (0,<£) obtained with the 
bar-type fuze, transverse excitation, are gen- 
erally greater than those obtained with the 
ring-type fuze. Furthermore, / 2 (0,<£) is gen- 
erally a slower function of 6 in the region 45 
to 90 degrees than in the region 0 to 45 de- 
grees, so that the average values obtained 
with the bar type depend less upon angle than 
with the ring type. At any one angle of in- 
cidence, however, the signal received by the bar- 
type fuze on a particular projectile tends to have 
a larger -spread than for the ring type, because 
of the spread in dipole orientation mentioned 
above. 

Antenna Gain. The equation (93) shows 
that M is proportional to the gain G of the fuze 
antenna. The values of G obtainable with pres- 
ent designs are relatively low, in the range 1.5 
to 3. For an infinitesimal antenna G = 1.5, and 
for a half-wave dipole G = 1.64. To get highly 
directive antennas the frequency used would 
have to be very much higher than used at 
present, because of the small allowable physical 
dimensions of the antennas. Because of this, the 
antenna gain to date has not been a major de- 
sign factor. 

Carrier Frequency. From equation (103) it 
is seen that the audio frequency of the im- 
pedance change is proportional to the carrier 
frequency. The amplitude of the impedance 
change is also affected by the carrier frequency, 
since M is proportional to A. Thus M is inversely 
proportional to the carrier frequency, while the 
audio frequency is directly proportional to the 
carrier frequency. Besides these direct effects, 
the carrier frequency affects M indirectly 
through its influence upon the directivity pat- 
tern (see Figure 23) and upon antenna gain. In 
addition to these important effects upon the 
impedance signal, it should be noted that the 
carrier frequency also affects the circuit effi- 


ciency and antenna matching, thus altering the 
values of S that can be achieved. This, however, 
is the subject of another chapter. 

There is a discreteness in the possible firing 
positions introduced by the use of the thyratron 
control circuit. The spacing of these discrete 
positions is determined by the carrier fre- 
quency. Figure 29 shows how the discreteness 
arises. 



Figure 29. Illustrating the discrete character 
of possible firing positions. Signal voltage is 
plotted against height. 

The solid curve represents the voltage out of 
the amplifier which is gMS having the dotted 
envelope gM 0 S 0 . The horizontal line B represents 
the holding bias. The point P, at which the en- 
velope intersects the holding bias line, repre- 
sents the point of function predicted by equa- 
tion ( 105) . The fuze actually functions when the 
M wave intersects the bias line at A a fraction 
of a cycle later. The positive peaks of the M 
wave occur for each A/ 2 reduction of the height. 
For a particular fuze the size of the M wave 
might be such that it just passes over one 
positive peak. The predicted height of function 
would lie near this peak but the actual function 
would not occur until near the next peak about 
A/2 further along. If the random variation of 
fuze sensitivities is larger than the change from 
one wave to the next, we will expect a random 
height of burst with bunches located at posi- 
tions roughly 1/2 apart. Thus the carrier fre- 
quency determines the separation of the discrete 
function positions. 

This discreteness has been observed in field 
trials. It implies that the average height of 
function should be about (A/4) less than the pre- 
dicted height. 




WORKING SIGNALS; GROUND-APPROACH CASE 


53 


Ballistic and Target Factors 

Distance from Target . It has already been 
shown that the magnitude of M is inversely 
proportional to the distance h of the fuze an- 
tenna from ground. (This has been derived 
from the consideration of the radiation field 
alone and is not valid for distances close enough 
so that the other components of the field are im- 
portant. The modifying effect of these com- 
ponents is considered in Section 2.10.) Thus a 
plot of the resistance component of the reflected 
impedance versus h will take the form of a 
hyperbola, upon which is superposed a sinus- 
oidal variation of space wavelength 1/2 and 
another variation according to $he changes in 
f 2 (6,<t>) as the fuze moves along its trajectory. 
This latter factor is essentially constant over 
the working range of any particular trajectory 
for the ground-approach application. 

Orientation of Fuze Antenna Relative to 
Target. The part played by the directivity pat- 
ten has already been described. The ballistics of 
the situation, however, determine 6 and <f> and, 
therefore, the use to which the directivity pat- 
tern is put. 

Because of a certain amount of rotation of the 
projectiles in flight, <f> is generally indetermi- 
nate ; for the ring type this is of no consequence, 
since the directivity patterns have cylindrical 
symmetry. The value of f 2 (0,<j>) for the bar- 
type fuze suffers a certain amount of indeter- 
minacy as we have seen. 

For bombs released from flight, the angle of 
incidence a increases as the speed of release in- 
creases and as the height of release decreases. 
This applies to dive bombing as well as release 
from level flight. 

For projectiles fired from ground, a increases 
as the angle of elevation decreases. The speed of 
projection also plays a part. 

In all cases the ballistic properties of the 
projectiles influence a in some degree because 
of the effect of air resistance. Tables of inci- 
dence angle a and vertical component of striking 
velocity are too lengthy to be included here. 
They may be found in standard bombing tables 
or in special tables prepared for use with VT 
fuzes. 18 ' 21 * 70 > 71j 74 

Speed of Approach to Target. It has already 
been shown that the audio frequency is pro- 


portional to dh/dt, the speed of approach to the 
target surface. This speed of approach is deter- 
mined by the release conditions of the pro- 
jectiles (angle, speed, and height) and by their 
ballistic properties, and is essentially constant 
over the last few hundred feet of flight. 

Now it happens that a and dh/dt are some- 
times so related that proper shaping of the 
amplifier can be utilized to make up for wide 
variations in a over a range of conditions, with 
the result that the height of function remains 
fairly constant over the range. This is con- 
sidered in detail in Section 3.2. 

Because of the usually high speed of ap- 
proach to the target, the amplitude of the M 
wave increases rapidly as the fuze nears the 
point of burst. Since the impedance changes 
are converted to voltage changes and then im- 
pressed upon an audio-frequency amplifier, it 
becomes important to take the dynamic char- 
acter of the signal into account in order to 
determine the output of the amplifier. This 
matter has been the subject of considerable 
study and will be discussed in Chapter 3. As 
already indicated, it can be stated that to a 
sufficiently good approximation we can usually 
utilize the steady-state characteristics of the 
amplifier in computations of the function point 
of the fuze. 

The terminal values of dh/dt encountered 
in the ground-approach applications range 
from about 200 to 1,200 fps. 18 Over the range 
of carrier frequencies 40 to 150 me, this repre- 
sents a range in audio frequencies of 16 to 
360 c. Only part of this range is encountered in 
any one application. 

Reflecting Properties of Target. The reflec- 
tion coefficient n has already been defined in 
Section 2.5.1. Using this definition the imped- 
ance signal received from various types of 
surface is proportional to n. Before going fur- 
ther the method of measuring n for various 
types of ground will be described briefly. The 
apparatus consists chiefly of an antenna similar 
to a longitudinally excited bomb, fed by a load- 
sensitive oscillator. When the height of the 
antenna above the reflecting ground is varied 
the radiation impedance of the antenna changes, 
these changes affecting the grid voltage of the 
oscillator in a manner given by equations (89) 


SECRET 


54 


THE RADIATION INTERACTION SYSTEM 


and (93). The amplitude of the fluctuations 
about the center value of grid voltage are re- 
corded. These fluctuations are then compared 
with those obtained in a similar experiment 
with a large metallic screen for ground. Since 
the metallic screen is practically a perfect re- 
flector (n = 1), the effective reflection coeffi- 
cient of the ground is given by the ratio of the 
voltage fluctuations for the two types of reflec- 
tor at the same height above each. Caution must 
be observed, in making these measurements, to 
use a large enough screen. The screen dimen- 
sions must be large compared to the maximum 
height used if complicated diffraction effects 
are to be avoided. 

The results thus obtained check well when 
used to compute the actual magnitude of the 
signal instead of ratios. They also check with 
published values of the reflection coefficient for 
plane waves. 17 ’ 27 

Table 3 shows the effective reflection coeffi- 
cients of several types of surface. 


Table 3. Reflection coefficient n. 


Surface 

n 

Fresh water 

0.8 

Salt water 

0.95 

Average earth 

0.5-0.6 

Ice 

0.2 


If the ground surface is smooth, the value of 
M is proportional to the reflection coefficient n 
defined above. For the reflection coefficient n to 
apply, the surface must be fairly homogeneous. 
Irregularities, such as stones, that are small 
compared with the wavelength will have little 
effect upon M when the fuze antenna is at 
least several wavelengths away. Areas, such as 
puddles, that have a different reflection co- 
efficient from the major part of the ground will 
likewise have little effect, if they are small com- 
pared to the height of function ; a sort of aver- 
age reflection coefficient is involved in such 
cases. 

The effect of superposed targets, such as ice 
over water, must be considered. Penetration of 
the radio waves at the frequencies used is quite 
small for metal, sea water, fresh water, dry 
sand, and ordinary soil. Penetration into ice 
or snow is considerably greater. Water a few 
inches deep over a considerable area of land or 


ice acts like a water target because of its small 
penetration of the waves into water. A layer 
of ice or snow that is only a few inches thick 
gives a reflection coefficient more nearly that of 
the surface beneath it than of ice or snow. 

The effect of a general slope in the target 
area is equivalent to a different angle of fall 
over level ground. 

The effects of large surface irregularities are 
complicated and must be evaluated empirically. 
When the fuze passes close to a large body, such 
as a building, the reaction is similar to that 
from an airborne target (treated in Section 
2.11), and the burst occurs near the obstruc- 
tion. 

The effect of built-up areas like cities on the 
height of burst is not yet well known. How- 
ever, some general remarks can be made. The 
general average reflection coefficient n will be 
lower than for moist earth, i.e., about 0.4. In 
general it is expected that the average height of 
burst will be greater than that predicted on the 
basis of the average n; the difference is about 
half the average height of the structures. The 
dispersion in height of burst will, of course, be 
considerably increased. 

The height of burst over densely wooded 
areas has been found by experience to be just 
below the level of the treetops for longitudinal 
fuzes. Not much is known about transverse 
fuzes under this condition. 

When the fuze passes near the edge of a cliff, 
it functions in a manner similar to the air- 
borne-target case. When it passes over a bound- 
ary between two different reflecting media such 
as water and sand, there is a change in M 
which is rapid if the fuze passes close to the 
boundary and slower if the distance is larger. 
Whether or not the transition causes a burst 
will depend upon the transient response of the 
amplifier and the abruptness of the transition 
between reflectors. 

2 10 EFFECT OF INDUCTION FIELD 
ON CLOSE FUNCTIONS 1 

The preceding analysis of the reflected im- 
pedance, based solely upon the radiation fields 

f Bibliographical references pertinent to this section 
are 12, 23-26, 39, 40, 94. 


SECRET 


EFFECT OF INDUCTION FIELD ON CLOSE FUNCTIONS 


55 


from the antennas involved, would indicate 
that there is no change in reflected impedance 
for the case of a longitudinally excited fuze 
approaching the ground in a vertical direction 
since f 2 (0) = 0 . However, a little thought will 
show that this is contrary to the principle of 
conservation of energy. Therefore we must call 
upon those fields in the vicinity of the antenna 
which die away as the square of the distance 
and the cube of the distance in order to de- 
scribe the behavior of the fuze near the ground. 

This can be seen as follows. If we use the 
same argument as used in Section 2.14 with the 
dipole oriented with its axis vertical, we find 
that the total power radiated through the upper 
infinite hemisphere varies with the height of 
the dipole. These variations must appear as a 
variation of radiation resistance and hence give 
rise to an M signal. The higher-order terms 
appearing in equation (160) (see Section 2.14) 
represent the effect of these nearby fields for 
the special case of the short horizontal dipole. 
It should be stressed that the calculation is 
made in terms of radiation fields alone but that 
the results are identical with a treatment based 
upon the induction and quasi-static fields . 23 

If attempts are made to extend this method 
to the more complicated radiation patterns of 
typical fuzes approaching at different angles, 
the necessary integrals become impossibly com- 
plicated and it is more convenient to use the 
actual fields to calculate the result. 


210 1 Second Approximation to the 
Field Equations 

In the previous discussion it was possible, by 
restricting attention to 1/r radiation fields 
alone, to avoid any reference to the current 
distribution of the antenna and its coupling to 
the feed system. In the argument which follows 
it will be necessary to assume a current distri- 
bution of a form which will give rise to the 
observed radiation pattern and to consider the 
interaction of this current with the reflected 
fields. We shall be interested in the case of a 
fuze approaching an infinitely reflecting ground. 
The case of the airborne target does not, in 
most cases, involve the nearby fields to a seri- 


ous extent and has not been considered from 
this point of view. As has already been shown 
we deal only with the fuze and its image to 
derive the necessary impedance change. 

The problem thus becomes one of calculating 
the mutual impedance of two identical antennas 



Figure 30. Representation of fuze antenna and 
its image. 

oriented as shown in Figure 30. In this figure 
we assume that the current distribution on 
each antenna is given by 

fi(^i) = hogM), (105) 

-Ufe) = hogzfa), (106) 

where I 10 and / 20 are the currents at the feed 
points. We are forced to assume that the pres- 
ence of either antenna does not alter the current 
distribution on the other and that both are 
identical, except for a 180-degree phase shift, 
and the same as the distribution when each 
antenna is radiating into free space. 

Now the current /i( 2 i) gives rise to a field 
# 21 ( 22 ) parallel to antenna No. 2 and vice 
versa. Following Carter 94 we write for the 
mutual impedance 

L 

Z\2 = — j— f # 21 ( 22 ) 02 ( 22 )^ 2 . (107) 

1 10 J 

0 

We first examine E 2 1 . For an infinitesimal dipole 
of length dz, the field at distance r is given by 

E S = b j^ S me[l-f r - - «, 

(108) 

E, = ^ cos 6 [- | - ^ 5 ] jet* - «, 

#0 = 0, 

where (3 = 2n/'k and b is a constant. At suffi- 


jiSEC] 


56 


THE RADIATION INTERACTION SYSTEM 


ciently large distances the higher orders of 
(1 /r) can be neglected, thereby making E r 
negligible and 


E e = -r— sin dje i(fat ~ pr) . (109) 

AV 

It was this field that was used in the previous 
analysis and called the radiation field, since it 
accounts for the average radiated energy. The 
other terms, in the integration of the Poynting 
vector, give fluctuating components of energy 
with no net energy flow. 

The above expressions pertain to an infini- 
tesimal antenna. The fields due to a finite an- 
tenna may be obtained by regarding the antenna 
as composed of infinitesimal antennas and inte- 
grating the fields due to the individual infini- 
tesimal antennas. 

For a finite linear antenna placed along the 
z axis, we have 


(HO) 

with a similar integration for E r . The integral 
sign here denotes the limit of a vector summa- 
tion over the whole antenna. 

Now r and 6 are in general functions of z. 
For points sufficiently distant from the antenna, 
the dependence of d upon z is sufficiently slow 
that it may be neglected. For comparatively 
large distances the r dependence upon z may be 
neglected in so far as the amplitudes of the 
contributions of the individual elementary an- 
tennas are concerned ; because of the finite 
propagation time, however, the individual con- 
tributions vary in phase. These phase variations 
cannot be neglected. Taking into account the 
above considerations, the components of the 
electric field may be expressed as follows : 


E e 


JA 


j(ut — 0 r) 


E r = b 


Xr 


jpjiut — 0r) 


[/ I Sr (/3r) 2 ] ' 


sin d J'e-tt 2 ™* 0 I(z)dz, (111) 


J e 


\r 


T- U - -1 1 

(0r)\| 


\- 2 J 

L 

cos d J'e-m*"** I(z)dz. (112) 


In the above expressions the factor e -jpz cos e 
takes into account the phase variations just dis- 
cussed, since z cos 6 is the path difference for 
contributions from z = 0 and z — z. The r in 
the above equations is the distance from the 
point z — 0 to the point P, where the field is cal- 
culated. The term I(z) represents the z de- 
pendence of the antenna current over its length 
L. 

If we denote the remote radiation field of the 
finite antenna by E Tad , equations (111) and 
(112) may be modified as follows: 


Ee [* ir (/Sr) 2 ] Er ° d ’ 
E r = cot 6 E„ 

L 

E ra d je^ wt ~ sin 6 j e ~^ z cos 0 


(113) 

(114) 


I(z)dz. 

(115) 


For thin antennas, sinusoidal current dis- 
tributions are often assumed as engineering 
approximations ; the integration may be effected 
under this assumption, giving well-known 
formulas for £ r ra(i for such cases. 

For the fuze antennas, the current distribu- 
tions are ordinarily not known with sufficient 
precision to allow the carrying out of this inte- 
gration. The 6 dependence of \E rad \ is obtained 
experimentally by the method described in Sec- 
tion 2.8.2. Thus the f(0) used there is given by 

L 

fid) = | sin 6 J' e~ j P zcos0 1(z)dz |. (116) 

o 

The experimental method gives only the ab- 
solute value as indicated and not the phase 
dependence on 6 which is ordinarily not needed. 

To get E 21 from E r and Ee we use 


E n = Eoi sin 0 2 “f - E r i cos d 2 - (117) 


The restrictions which allowed us to write equa- 
tions (113) and (114) also imply that <9 2 = Oi 
and that both are sufficiently independent of 
z 1 and z 2 . Thus we write 


E 2 1 = E e sin 6 + E r cos d = E21 e^ 1 ~ *>, (117a) 

which defines E 2 i as a function which is inde- 
pendent of z. In the exponential term r is the 


EFFECT OF INDUCTION FIELD ON CLOSE FUNCTIONS 


57 


distance from z 1 = 0 to the point 2 2 on antenna 
No. 2. Thus the mutual impedance becomes 

L 

Z 21 = — j— E 21 J' e~ J P r gziz^dzz. (US) 
0 

Again we must take account of phases, and so 
we denote r as the distance between the point 
z x = 0 on antenna No. 1 and the point z 2 = 0 on 
antenna No. 2. In this notation r = T z 2 cos 0, 
and we can further simplify equation (118) to 
get 

L 

Z 2i = —~E 2 ie~ jp ' r f e~^ Z2COse g 2 (z^)dz 2 . ( 119 ) 

iio J 

0 

If we neglected all induction fields in the cal- 
culation of equation (119), the only change 
would be that E 21 ' would reduce to E' raa sin 0 
where F7' rad is defined in the same manner as 
E 2 i. If we call the result of such a calculation 
Z 2 i rad , we have 


E*’ 

E' sin Q ’ 

rad 


( 120 ) 


or, since M 0 is proportional to Z 21 , we may write 

M 0 _ \E 21 '\ 


Mo 


I E' sin ^ | 

1 rad 1 


(120a) 


Comparison of equations (113), (114), (120), 
and (121) shows that 

Mo 

Mo 


V f 1 ~ w? - m * cot29 ] + \jr + i cot2fl ] ’ 


which reduces to 


= T 1 _ w 2(4cot40_ x) ]’ (121) 

rad L- - 1 

after expanding and dropping inverse fourth- 
power terms in r. 


2102 Effect of Induction Field on 
Function Heights 

Equation (121) is a second approximation to 
the calculation of Z 12 . It is not exact and is 
limited in its application to cases where the 


antenna is close enough to its image to make 
the nearby fields appreciable but not so close 
that the approximations used in deriving it 
break down. Thus it can be expected to give 
reasonably valid answers only for heights such 
that the antenna length is not a considerable 
fraction of the distance between it and its 
image. Moreover, the whole derivation is based 
upon a thin wire antenna as a model. The fat 
antennas actually used may alter conditions. 

Actually, in spite of the limitations, the 
theory has been of considerable use in proper 



Figure 31. Contribution of induction and quasi- 
static fields to height of function; H t as func- 
tion of Hr for various values of 9. 


selection of fuze antennas and the selection of 
proper operating frequencies. 

Since \dV\ is proportional to M 0 , we can then 
say 



dVr 


Mo 

Mo 


( 122 ) 


where \dV r \ is the peak value of the voltage 
change into the amplifier that would be com- 


SECR 



58 


THE RADIATION INTERACTION SYSTEM 


puted from radiation fields alone and \dV t \ is 
the total voltage change including the effect of 
nearby fields. If we now set \dV r | and \dV t \ 
each equal to the signal magnitude required to 
actuate the fuze, B/g, the heights of function 
predicted with and without the correction 
terms, denoted by h f and h r respectively, are 
seen to be related as follows : 


s + ~ "■ (123) 

This relation is shown graphically in Figure 31 
for several values of 0. This graph shows the 
contribution made by the induction and quasi- 
static terms to the heights of function. This 
contribution is seen to be significant when 0 is 
small and when h t /k is small. For large values 
of 6 and (h t /k) the correction becomes negli- 
gible. 

If we use H r as the height of function, ex- 
pressed in units of k as calculated without the 
correction, and H t as the height of function in 
the same units and including the corrections, we 
may write 

h, = H r [y 2 + y 2y Ji + ' (124) 

where 


D = 


4 cot 4 0—1 
4 tt 2 


(125) 


For a vertical approach H r = 0, but the cor- 
rection term becomes infinite leading to an inde- 
terminate answer for H t which must be evalu- 
ated by further means. 

From equation (104) we see that 

Hr = tt nSo B f2( - e) - (126) 

Also from equation (116) we see that 

L 

f\S) = | [sine / 1(z)dz |] 2 . (127) 

0 

Since the integral is a slowly varying function 
of 6 for small 6 , we may write 


P(6) = a sin 2 6, (128) 

for very small angles. For any particular pro- 
jectile the value of the constant a is determined 
experimentally from its measured directivity 


pattern. Combining equations (124), (125), 
(126), and (128), we get for very small angles 


or 



(129) 



The latter value is independent of 6 and suffi- 
ciently accurate for 0 from 0 to 10 degrees. It 
is not valid for H t < 1 ; in such cases the theory 
does not hold anyway, as has already been 
mentioned. 

The equation (129a) is of interesting quali- 
tative value, since it shows that the height of 
burst at very steep approach angles depends 
upon the slope a of the directivity pattern near 
0 = 0 (slope on sin 2 0 paper). Thus directivity 
patterns like curves 5 or 6 in Figure 25 will 
give very low height of burst even with the aid 
of the induction field. 

Figure 31 may be used to correct the heights 
of function computed on the basis of radiation 
alone. Referring to the example worked out in 
Section 2.9, we have H r = 20/8.2 = 2.4. From 
Figure 31 we see that for 0 = 18.5 degrees and 
H r = 2.4, H t = 2.7, or h t = 22 ft. 

In this case the correction is not large. For 
steeper angles of approach the correction be- 
comes more pronounced. If radiation calcula- 
tions predict a height of 2k for a striking angle 
of 10 degrees from the vertical, the actual burst 
height will be 3.5 k, a correction of +75 per cent. 

A large amount of computation of heights of 
function has proved to be necessary. For this 
reason a method has been developed which 
greatly reduces the amount of labor involved, 
especially when rapid computations are needed 
in order to help design an amplifier with a 
shaping such as to give desired heights of func- 
tion over a large range of ballistic and fuze 
conditions. This method involves the use of 
transparent charts. 39 

We see from equation (129a) that for steep 
approach the height of burst varies as the 
square root of the burst control factors, G, n, 
S, g, and 1/B, and is thus less dependent upon 
variations in these quantities when burst 


SECRET 


WORKING SIGNALS; AIRBORNE TARGET 


59 


heights are such that the induction field is 
predominant. 

A word of caution is necessary about incor- 
porating amplifier delay to avoid noise troubles 
on fuzes where the induction field is the pri- 
mary signal controlling the height of burst. 
Suppose, for example, we have a fuze on a 
small antenna so adjusted that S = 15, g — 50, 
and B = 4.5. Then for average ground n — 1/2, 
and for the small antenna a = 1 and G = 1.5. 
When these values are inserted in equation 
(129a) the result is 

H t = 1.3. 


an understanding of the operation. In Section 
2.11.1 we shall consider the target to be a small 
sphere which reflects equally in all directions. 
First we consider the changes in phase in the 
M wave and later the amplitude changes. Sec- 
tions 2.11.2 and 2.11.3 will be devoted to a dis- 
cussion of actual airplane targets. In all discus- 
sions we use a reference system at rest on the 
target. 

2 11 1 Properties of the M Wave; 

Simple Theory 


If the firing level of the amplifier lags as 
much as 3 c behind the calculated input firing 
level, the fuze will reach H t = Q before the burst 
is initiated, since there are 2 c of input voltage 
per 1 change in height. Such delay may give rise 
to duds because the fuze breaks up before the 
firing pulse is received. This behavior has been 
observed in special fuzes carrying integrating 
circuits to increase the resistance to noise pulses 
and sweep jammer signals. 


211 WORKING SIGNALS; 

AIRBORNE TARGET^ 

The preceding two sections have been de- 
voted to an analysis of the signals encountered 
in the ground-approach case. The second im- 
portant application of a radio proximity fuze 
is to initiate bursts in the vicinity of an air- 
borne target. In the present section the signals 
occurring in this case will be studied. 

To avoid complication we assume that the 
fuze and target are far from ground and under- 
stand that corrections may be introduced if 
they are near the ground (see Section 2.5). 

It is, of course, to be expected that the re- 
flection from so complicated a target as an air- 
plane will indeed be complex and not amenable 
to exact analytic treatment. There are, how- 
ever, certain general features of the problem, 
which can be discussed in terms of a simple 
model, that carry over into the actual problem. 
A knowledge of these features is essential to 

s Bibliographical references pertinent to this section 
are 1, 14, 15, 55, 61, 72, 73, 75, 93. 


Phase Properties 

Figure 32 represents the spatial arrangement 
of fuze and target (a small sphere). In this 










TRAJECTORY 


Figure 32. Spatial arrangement of fuze and 
small spherical target. 


figure the axis of the projectile is shown as 
coinciding with the trajectory. This is, of 
course, not time in the general case but is close 
enough for the type of approach used in firing 
rockets in air-to-air combat, since deflection 
firing is seldom considered. The projectile is at 
P and is moving along the x axis in the direc- 
tion of the arrow. The distance between projec- 
tile and target is r, and the shortest distance 
between the target and the line of flight of the 
projectile is p. The term p may be called the 
impact parameter as in similar situations in 
atomic physics. The line OQ is perpendicular 
to PQ. The distance from P to Q is x. The angle 
between PO and PQ is a. For fuze systems in 
which the body of the projectile is used as the 
antenna (longitudinal excitation), the angle a 
is the same as the 6 previously defined. The 
relative velocity of the projectile along its line 
of flight is denoted by v. 


SECRET 


60 


THE RADIATION INTERACTION SYSTEM 


To proceed further, we recall that for the 
case of reflection by a simple airborne target, 
the M wave is given by a function of the form 

M = M 0 e^~ 4 ^ + 5 k (130) 

There may be a phase shift at reflection which 
will be a constant for the spherical target and 
will be neglected. 

The frequency F of the M wave is 

F 

F 

F = ~ cos a. (132) 

A 

Thus the maximum possible value of the in- 
stantaneous frequency is 2v/l when a = 0 de- 
grees when the target is very far away, and the 
minimum value is 0 when a = 90 degrees. As 
the projectile approaches the target the fre- 
quency decreases; when the projectile is at the 
point of nearest approach to the target, the in- 
stantaneous frequency is zero. 

The rate of change of instantaneous fre- 
quency with angle is given by 


J_ I d/^irr\ 
2 tt j dty X J 

2 I dr I 
X \dt\ 7 


(131) 


dF 2v . 

— = — v si 
da X 


(133) 


This equation indicates that the rate of 
change of instantaneous frequency increases 
as a approaches 90 degrees. For sufficiently 
large values of a, the rate of change of fre- 
quency with angle is great enough to cause a 
considerable change of instantaneous frequency 
during the course of 1 c. Thus it is important 
to introduce dynamic considerations when 
studying the response of an audio amplifier to 
such a signal. 

It should be pointed out that there are in gen- 
eral only a relatively small number of waves of 
M in that part of the trajectory where the fuze 
is sufficiently near the target to be effective. 
Calculation gives the result that there are 
0.8 p/X waves in the region from a = 45 degrees 
to a = 90 degrees. 

For a typical case X = 8 ft, p = 50 ft, and 
there are 5 c in the M wave. A longer wave- 
length means fewer cycles and requires more 
care in including dynamic considerations in the 


study of the behavior of an audio-frequency 
control circuit. 

Caution must also be observed, in incorporat- 
ing delay to avoid noise troubles and interfer- 
ence from jamming signals, to make sure that 
enough cycles are available to actuate the con- 
trol circuit. Thus the higher the carrier fre- 
quency the larger the number of waves avail- 
able and hence the better a control mechanism 
based on audio-frequency selectivity can be ex- 
pected to function. 

The manner in which the resistive component 
of the reflected impedance changes as the fuze 









THEOf 

1ETICAL SIM 

PLE ENVEL0I 


/ / ‘ 



EDT 



4 1 0 



lLLLlX 

OBSERVE 

:0 ENVELOPE 

Sc 





0BSE 

RVE0 M WAVE'' N 

\ 

1 

1 

1 


1 1 

1 

c 

14 12 1 

1 L 

0 

1_ 

1 

6 

N 

1 

O 


i i i i i i i i i 

85* 40* 45* 50* 55* 60 * 65* 70* 75* 80* 


Figure 33. Typical experimentally observed M 
wave, with its envelope and theoretical simple 
envelope. 

antenna moves along its trajectory is shown 
qualitatively by the dotted line in Figure 32. 


Amplitude Properties 

From equation (94) we see that 

Af° = A -L Gf\a) cos r. (134) 

Figure 33 shows a plot of M 0 for a spherical 
target with / 2 (a) the actual measured directiv- 
ity of a typical fuze. It is marked “theoretical 
simple envelope” on this figure. The ordinates 
represent the M signal in arbitrary units. There 
are two sets of abscissas, one set representing 
—x/l, as defined in Figure 32, and the other set 
representing a. 

It will be observed from equation (134) that, 
as the target is approached, M 0 increases as the 
square of the distance decreases and as the 


SECRET 


WORKING SIGNALS; AIRBORNE TARGET 


61 


directivity in the direction of the target in- 
creases. We shall expect this general sort of 
behavior even for a complicated target. 


2,11,2 Reflecting Properties of Aircraft 

When considering a complicated reflecting 
target like an airplane we shall expect a varia- 
ble phase shift upon reflection. This we repre- 
sent by assuming that A, as defined in Section 
2.5.2, is complex and of the form 

A = F(r,d,<t>)eM r > 0 ’*K (135) 

At very large distances, such that the wave in- 
cident on the target can be considered plane, 
equation (135) will reduce to 

A = (136) 

the 1/r dependence of reflected field being taken 
care of in the definition of A. At close distances 
the whole argument becomes too complicated to 
be within the scope of this report. 

The variation in the phase of M arising from 
5 (0,$) will change the spacing of the zeros 
of M and thus alter the apparent instantaneous 
frequency in a complicated manner. 

It is helpful to consider the airplane as a 
complicated antenna which is excited by the 
incident radiation and which reradiates with a 
many-lobed pattern characteristic of such an 
antenna. Whenever the direction of the incident 
radiation changes, the distribution of current 
on the aircraft changes and the radiation pat- 
tern is correspondingly altered. Moreover, if 
the source of radiation is close so that the field 
is not uniform over the target, the distribu- 
tion of current will change with distance, also 
giving a change in the reradiation pattern. 

We might expect that the dependence of A 
and 5 upon r will disappear for distances r such 
that the target does not fill more than the first 
Fresnel zone. We define the first Fresnel zone 
in this case as that circular area such that the 
path from the fuze to the center of the area is 
X/4 shorter than the path from the fuze to 
the outer rim. Experiments to be described 
later show that this is roughly borne out. 

For frequencies of 100 me and a target 50 ft 
across, the target just bridges the first zone at 


r — 125 ft. The radius of action of present-day 
fuzes is well inside this range, so that simple 
calculations can only give an order-of-magni- 
tude effect. The actual values of M must be de- 
termined by experiment. 

There is, however, one very important factor 
that minimizes the effect of the complicated 
reflection on fuze performance. The factor 
f 2 (a)/r 2 grows so rapidly with increasing a 
that there is a relatively small region in space 
around the target where the signal is large 
enough to actuate the fuze and the point of 
burst becomes relatively independent of the 
details of the wave form provided there are 
cycles enough to get through the amplifier. 

Experimental Measurement of Reflection 
from Aircraft 

The straightforward method of measuring 
the reflecting power from an airplane is to con- 
struct fuzes carrying radio reporting circuits 
and fire them past an airborne airplane. This 
gives the actual working signal but technical 
difficulties make such tests impossible at the 
present time. 

For certain special interaction conditions the 
airplane can be flown past the fuze, which is 
held fixed in space. This gives information 
which is useful for head-on or tail-on shots in 
air-to-air combat; these are the most common 
shots where rockets are concerned. 

Experiments have been made for these con- 
ditions in two ways. (1) The fuze was sus- 
pended beneath a blimp and the airplane flown 
by it. These tests gave reliable qualitative in- 
formation about the signal voltages, but it was 
difficult to get the exact distance measurements 
required. (2) The fuze was supported at a 
height of X/4 over a reflecting screen on the 
ground and an airplane flown over it. 1 These 
latter experiments were made at the Naval 
Proving Ground, Dahlgren, Virginia. 

Properties of the Experimental M Waves 

Some 50 space patterns were obtained from 
which quantitative measurements could be 
made. Parts of three typical patterns are shown 
in the oscillograms of Figure 34. In Figure 33 
a typical experimentally obtained pattern is 
shown, together with its envelope, which is 


62 


THE RADIATION INTERACTION SYSTEM 


compared with the theoretical simple envelope 
discussed above. 

An analysis of the phase properties of the 
experimentally obtained waves gives very good 
agreement with the simple theory given in 
Section 2.11.1, showing that 5 (<9,<£) is a slowly 
varying function and does not complicate the 
pattern. 

The experiments also showed that the inverse 
square law holds. The upper curve in Figure 35 



Figure 34. Oscillograms of parts of typical M 
waves in fly-over tests. 

These oscillograms were obtained in tests in which an 
airplane flew over a fuze antenna mounted horizontally 
above the ground. In the figures time increases from the 
left to right. The vertical lines are timing pulses. The three 
oscillograms are parts of a large photograph discussed on 
page 23 of reference 1. Details of test conditions will also 
be found in this reference. 

shows the results of a series of tests in which 
an SBD-1 airplane flew vertically over a fuze 
antenna; the plane was in horizontal flight 
parallel to the axis of the fuze antenna. The 
fuze antenna was a distance X/4 above the 
screenwire ground. The ordinate in Figure 35 
is the logarithm of the magnitude of the signal 
voltage AF, and the abscissa is the logarithm 
of the distance p. It is clear from the figure that 
the inverse square law holds for distances as 
close as 80 ft for X = 7.4 ft as used. 

From the Dahlgren experiments some quanti- 
tative comparisons were made of the reflection 
from the best aspect of the airplane and the 
reflection from a tuned half-wave dipole. The 
dipole was placed horizontally at various heights 
above the fuze antenna and turned about a 
vertical axis. As the dipole was rotated about 
a vertical axis, the reflected impedance M 0 
changed from zero to a maximum value as cos r 
varied from 0 to 1. The signal magnitude at 
various heights was taken. Typical results are 
shown in the lower curve in Figure 35. The 
ordinate distance between the upper and lower 
curves in Figure 35 represent a ratio of 21 ; 


that is, the reflecting power of the airplane in 
the aspect considered is 21 times as great as 
that of a tuned half-wave dipole arranged for 
maximum reflection. It has already been men- 
tioned in Section 2.5 that the reflecting power 
A max of a flat plate of area L 2 is L 2 X, whereas 
that of a tuned half-wave dipole is 0.26A. The 
projected area of the airplane, regarded as a 
flat plate, is about 300 sq ft. The wavelength X 
used in this experiment was 7.4 ft. Then the 
ratio 



becomes 20.5, in satisfactory agreement with 
the experimental values. 



Figure 35. Signals from airplane and from 
tuned half-wave dipole. 


Expressing the reflecting power of the air- 
craft in units of “dipoles” in the direction of 
maximum reflection has been convenient in en- 
gineering the fuze design. In the above de- 


SECRET 


WORKING SIGNALS; AIRBORNE TARGET 


63 


scribed experiment, the airplane is equivalent 
to 21 dipoles. 

The envelope of the wavy curve in Figure 33 
gives a rough idea of the variations in M 0 as 
the position of the fuze antenna changes with 
respect to the airplane target. This wave repre- 
sents the signal received by a radio fuze on a 
rocket due to a small airplane passing the 
rocket at a distance p equal to about 15A or 
105 ft in this case. To indicate the extent to 
which the signal acts as would be predicted 
from a point target, an envelope computed ac- 
cording to the simple theory is plotted on the 
same graph. That is, the simple envelope is a 
plot of the equation 

M 0 = Constant X - (137) 

whereas the observed envelope is effectively a 
plot of the equation 

Mo = Constant X ^ . (138) 

The two envelopes are adjusted so that their 
maximum values coincide. The observed enve- 
lope indicates the nature of the variation in A 
along the trajectory. It is clear from the figure 
that the simple features of the theoretical en- 
velope are modified in the observed envelope, 
in that there is a minimum around a = 60 de- 
grees, whereas the amplitude of the theoretical 
envelope rises constantly as a increases toward 
90 degrees. 

Other patterns experimentally obtained for a 
variety of aspects and distances exhibit similar 
features, that is, a general trend as expected 
from the simple theory, plus a superposed effect 
of one or two minima. The positions of the 
minima vary with aspect and type of airplane. 
Thus the amplitude properties of the wave fol- 
low the simple theory to a certain extent ; fur- 
thermore, as we have seen, the phase properties 
follow the simple theory quite well. Thus the 
characteristics of the wave are sufficiently well 
known to achieve good burst control, as will be 
shown in Chapter 3. 

Specification of Sensitivity Requirements 
for Plane-to-Plane Rocket Fuze 

We are now in a position to outline a 
sample calculation for a trial design center for 


a fuze for the plane-to-plane rocket application. 

The fuze will fire when 

M. - A (139) 

Within engineering limits, the quantity B/S 0 g 
can be varied at will, so we shall calculate the 
value of M 0 to be expected and leave the discus- 
sion of B/Sog to appropriate chapters. The 
maximum value of M 0 has been seen to be equiv- 
alent to about 20 dipoles for the direction of 
best reflection from the airplane. We take the 
value of 10 dipoles as a working average. 

From equation (49) we see that A for a sin- 
gle dipole is 0.26A, and with the aid of equation 
(134) we find the reflection from a target of 
10 dipole strength to be 

Mo( 90°) = ^p/ 2 ( 90°), 

at the point of maximum reflection from the 
target. For a typical fuze with a half-wave an- 
tenna G = 1.64, / 2 (90°) = 1, and X = 7.5 ft. 
If we wish the fuze to function up to a distance 
of p — 10X, 

M 0 ( 90°) = 2 ' 6 2 ^ - ' - 4 - = 0.007. 

If, however, it is desired to have the burst occur 
when a is approximately 60 degrees, for an as- 
sumed maximum fragmentation density in that 
direction, / 2 (60°) is about */2 and 

r 2 = _eL. = lE 2 

sin 2 a 3 

These values make 

M 0 { 60°) = 0.0026. (140) 

Experiments have shown that the loss asso- 
ciated with the dynamic response of shaped 
amplifiers is about 10 per cent. Thus we reach 
the final conclusion that a workable fuze must 
function when 

Mo ^ 0.0025. (141) 

To refine the calculation further would be 
useless, since the answer is only approximate. 
Trial fuzes were built to fire when M 0 = 0.0025 
and tested against a mockup target. It was 

found that this value gave good field results, 

the final proof of any design. 


64 


THE RADIATION INTERACTION SYSTEM 


It will be noted that the reciprocal of the 
value of M 0 required to fire the fuze is a meas- 
ure of the overall sensitivity of the device. It is 
convenient, as an aid to thinking, to specify this 
value in terms of a special type of test. We 
imagine the fuze moved toward an infinite per- 
fect reflector at such a speed that the doppler 
frequency is exactly right for maximum ampli- 
fier gain. We also assume the projectile to be so 
oriented that the direction of maximum radia- 
tion is toward the reflector. Under these special 
conditions 


M o = 


XG 
4 irk’ 


(142) 


and the fuze will function at a height h, given by 


, 

ItWo 


(143) 


For the calculation just outlined above this re- 
duces to 


^eff — 


7.5 X 1.64 
4tt X 0.0025 


^ 400 ft. 


For a quick specification of the overall fuze 
performance this effective height is quite con- 
venient. This method of specifying the sensi- 
tivity of a fuze is called the Michigan sensitivity 
and was used extensively by Section T, Office of 
Scientific Research and Development. 

Experience resulting from tests against a 
mockup target as well as against actual targets 
has shown that fuzes with h ett = 400 ft are 
quite satisfactory, but that greater sensitivity 
can be used with increased effectiveness. Values 
as high as 800 to 1,000 ft have been achieved in 
later models. 

The effective height as defined above should 
be used only for comparing the effectiveness of 
fuzes working on a given frequency. As seen 
from equation (143), h ett is proportional to X. 
On the other hand, for an airplane target, M 0 is 
not proportional to X but to a first approxima- 
tion is proportional to XL Thus for smaller X, 
h ett is reduced while performance against an 
airborne target is not reduced in proportion 
(see Section 2.11.3 following). 


21 13 Effect of X on Reflection from 

Aircraft 

Equation (134) shows that for all other con- 
stants equal 

M 0 ~ AX. (144) 

Mott 93 has calculated the values of A for vari- 
ous simple reflectors and finds 

Dipole: A ~ X 1 . 

Sphere: A ~ X°. 

Flat plate: A ~ X -1 . 

Considering all factors, he recommends as a 
working average value A ~ X~L Equation (144) 
then becomes 


M o ^ X* 

as an average case and M 0 ~ X° for the case of a 
flat sheet like an airplane wing. Our fuze ex- 
perience indicates that the behavior is more 
nearly the latter than the former. 


SIGNAL SIMULATION 11 


2.12.1 Properties Required of Simulator 

In the preceding sections a description of the 
impedance signal due to a reflector has been 
given, and it has been shown that the changes 
in amplitude and phase of the impedance sig- 
nal M are duplicated as amplitude and phase 
changes in dV. 

The value of M is a function of position alone 
and can be represented as a space pattern along 
the trajectory. This space pattern has been 
called the M wave. The value of M as a func- 
tion of time is obtained once the position is 
known as a function of time. The form of the 
M wave is not altered by the velocity of ap- 
proach; the wave is merely traversed at an 
appropriate rate. This means that it is possible 
to measure the M wave point by point with 
static impedance measurements and compute 
its time variations in any given case from the 
specified relation between position and time. 

h Bibliographical references pertinent to this section 
are 3, 7, 35, 46, 76, 92. 


SECRET 


SIGNAL SIMULATION 


65 


If we are to simulate the working impedance 
signal, we must devise an arrangement which 
presents to the fuze circuit an impedance which 
has the correct amplitude and time dependence. 
We are not concerned here with a device which 
attempts to simulate the vibration and stress 
conditions encountered by the fuze in actual 
use. 

Experience has shown that the r-f part of 
the fuze system is able to respond to changes 
of antenna impedance much more rapidly than 
any encountered by the fuze in practice. This 
means that the audio-frequency circuit is the 
part of the fuze that responds to velocity 
changes. As a result of this division of func- 
tion, it has been found desirable to test the 
r-f system and audio system separately in en- 
gineering the fuze design. A final test which 
simultaneously measures the combined per- 
formance of the complete system serves as an 
overall check to insure that there are no unde- 
sirable interactions. 

A truly faithful simulator must actually re- 
produce the rotating impedance vector which 
is characteristic of the interaction with the 
moving target. However, it will be seen in 
Section 3.1.7 that the sensitivity of the r-f cir- 
cuit to reactance changes is usually negligible in 
comparison with the sensitivity to resistance 
changes, so that a simulator which reproduces 
the resistance component of M is adequate for 
most work. This simplifies the simulator prob- 
lem greatly but it must always be remembered 
that an approximation is involved when such a 
“resistance simulator” is used. 

Additional properties that a simulator must 
possess are those which make its use practical. 
It must have a sufficient range of operating 
conditions, it must be reproducible, it must be 
convenient to use, and it must not introduce 
complicating disturbances into the fuze circuit. 


2 12 2 Field R-F Simulator 

There is one convenient method of simulation 
of the true antenna impedance variation that 
involves the use of a field setup. It is in fact not 
a simulator in the true sense of the word, since 
it reproduces the actual voltages as a function 


of distance from the target but not on the 
proper time scale. It is, however, discussed here, 
since it is one method for presenting the proper 
antenna variations to the r-f system. We refer 
to what is commonly called a “pole test.” 

In making pole test measurements, a fuze is 
mounted in a mockup of the proper projectile 
and suspended over a large reflecting screen by 
ropes attached to tall poles. The height above 
the reflector is varied, and point by point read- 
ings of the voltage ciV are recorded. The re- 
quirement for proper antenna simulation is 
automatically fulfilled. 

If the readings are taken at a height of sev- 
eral A, M 0 is quite small, and we can say that 

(145) 

except for a fixed phase shift which has been 
neglected. If calculated values of M 0 are sub- 
stituted in this expression, S 0 can be calculated 
for a given r-f circuit. 

In practice it is difficult to obtain the read- 
ings at a very large height so that M 0 may be as 
large as 6 to 10 per cent. It can be shown that 
the error in S 0 calculated in this manner is 
about the same size as M 0 . Such measurements 
are accurate enough for most purposes. 

There is apt to be a large error in pole test 
measurements if the reflecting screen is not 
large enough. When the height of the fuze be- 
comes comparable with the semidiameter of the 
screen, diffraction effects set in which are of 
unknown phase and magnitude. Errors as large 
as 100 per cent have been observed. It is de- 
sirable to have the screen diameter at least four 
times the height of measurement. 


2 12 3 Laboratory R-F Simulators 

By laboratory r-f simulators we mean those 
devices which generate impedance changes of 
a form suitable for making tests of the com- 
plete r-f system, but which do not have the 
amplitude-time dependence necessary for test- 
ing a complete fuze system. They fall into two 
general categories, those which vary the re- 
sistance component alone and those which set 
up the true rotating impedance vector. The 


dV = M 0 Sq sin I 


: SECRET \ 


66 


THE RADIATION INTERACTION SYSTEM 


latter, while interesting, do not give enough 
additional information on present-type fuze cir- 
cuits to justify their construction. Both types 
will be discussed briefly. Since the fuze circuits 
used at the present time have small reactance 
sensitivity, there has been no need for react- 
ance simulators, and none has been designed. 
However, as will be pointed out, the reflecting 
dipole simulator can be used as a reactance 
simulator if desired. 

Resistance Component Simulators 
(Substitution) 

This is the simplest of all tests to make in the 
laboratory. One merely disconnects the fuze 
antenna from the circuit and adds a dummy 
antenna consisting of lumped resistors and 
condensers, which duplicate the operating point 
of the r-f system. The resistance is varied by 
substituting several resistors in succession. A 
curve of V versus In R p (or In R s ) is plotted, and 
the slope of this curve at the operating point is 
the sensitivity S p (or S s ). 

If desired, the fuze assembly can be placed 
inside a shield can instead of removing the an- 
tenna exciter. Such an arrangement leaves the 
operating point reactance practically unaltered, 
and resistors can be substituted directly across 
the feed point. This latter method is preferable, 
since any stray coupling between oscillator and 
antenna is left undisturbed. 

Figure 36 shows a typical load curve obtained 
from such a series of measurements. It is a 
curve of V versus R p on a logarithmic scale. 
From such a curve S p , which has been defined 
as dV/d In R p , may be found. 

Resistance Component Simulators 
(Dipole Reflectors) 

The dipole reflector is not strictly a resistance 
simulator, since it can be made to perform as a 
rotating vector simulator, resistance simulator, 
reactance simulator, or combination simulator. 

We may see with the aid of equations (48) 
and (94) that the reflection from a half-wave 
dipole oriented so that / 3 2 ( 03 i, 4 > 3 i) = 1, is given 
by 

M = cos’ 

(146) 


We see that M can be changed by changing r, 
Z 33 , /i 2 (0i3,</>i3) , and t. All these changes have 
been utilized at one time or another. The dipole 
is adjusted so that 

Z 33 = (R s z + Zl), (147) 

where Z L is the external impedance connected 
to the feed terminals of the dipole. If we short 
the terminals, Z L = 0, and Z 33 reduces to R s3 . 

Wand. A wand consists of a length of wire 
cut to resonant length. In effect Z L = 0, since 
the terminals are shorted. It can be used in two 
ways. First, it can be oriented so that t — 0 and 
moved toward or away from the fuze antenna, 
thus varying r. When so used the signal pre- 
sented to the fuze is truly the rotating vector, 
and the changes dV can be recorded as the 
wand is moved. 

Second, it can be so located that M is purely 
resistive, t may then be varied by twisting the 
dipole in a plane perpendicular to r, thus vary- 



I 2 3 4 567 89 10 20 30 40507090 

R THOUSANDS OF OHMS 
P 

Figure 36. Typical loading curve. 

ing the effective resistance. If desired, the 
dipole can be attached to a motor so that t = co t. 
Then an audio signal will be developed which 
varies as cos 2 co£. 


SIGNAL SIMULATION 


67 


If reactance simulation is required, r may be 
adjusted so that M is purely reactive and the 
rotation gives a reactance variation instead of 
a resistance variation. 

Modulated Dipole . The term Z L can be varied 
by connecting a variable impedance to the ter- 
minals of the dipole. The variable impedance 
can be provided by a rotating condenser, com- 
mutator, flashing thyratron, or any other con- 
venient form of variable r-f impedance. Unless 
the variable impedance can be made purely re- 
sistive or purely reactive, the resulting M be- 
comes quite complicated because time-varying 
phase shifts arising from changes in Z L are 
included in the reflector. 

When dipole simulators are used in the lab- 
oratory, stray reflections set up complicated 



Figure 37. Basic circuit for diode simulator. 

standing waves in the room, and only qualita- 
tive answers are obtained. A change of position 
of the dipole with respect to the fuze varies 
f 2 (0,<f > ) and gives crude information about the 
directivity of the fuze. 

Such devices are useful for quick checks to 
see if fuze circuits are “live” and have approx- 
imately the desired sensitivity. Because of the 
(k/r) 2 factor in the reflection the device can 
not be used effectively at a large distance from 
the fuze and hence cannot be used well for 
measuring directivity patterns. 

Resistance Component Simulators (Diode) 

The a-c input resistance of a linear diode 
voltmeter is a function of the d-c resistance and 
d-c voltage in its load circuit. The fundamental 


circuit for a diode simulator is shown in Fig- 
ure 37. 

Terminals TT are connected to the antenna 
terminals of the fuze circuit. The reactance X 
represents lumped reactance (including a d-c 
return, if necessary) to make the input react- 
ance of the device simulate the operating point 
reactance of the fuze antenna. 

By varying v and R L the apparent r-f re- 
sistance R between terminals TT can be con- 
trolled. In practice R L is adjusted to give the 
value of R at the operating point when v = 0. 
The term v is then varied at an audio-frequency 
rate to introduce small periodic variations in R. 

If the diode is working in its linear region so 
that a d-c voltmeter indicates a voltage V across 
R l of several volts, the simple diode theory 
works quite well. Let R p be the dynamic re- 
sistance of the diode and 6 the semiangle of 
flow when v = 0. If v/V«l it can be shown 
that 

dR vR . v , 

y^^(2 cos 0) -y p, (148) 

where 6 is determined by 


R p 6 — cos 6 sin O’ y ' 

and subsequently Rl is determined by 

= - (tan 6 - 0). (150) 

■tl L TT 

Figure 38 shows the appropriate values of R L 
to give the desired value of R when R p is known, 
and the value of Pf the correction factor that 
must be applied to v/V to give dR/R. 

It is not wise to use values of R/R p less than 
10. If lower values of R are needed, a fixed re- 
sistance can be shunted across the circuit, with 
X and the ratio of v/V adjusted accordingly to 
make the overall dR/R have the desired value. 

The diode simulator need not be connected 
directly to the antenna terminals but may be 
capacitatively coupled, if appropriate calcula- 
tions are made and provided the diode is oper- 
ated in its linear region. 

In laboratory work it is advantageous to cali- 
brate the simulator directly by attaching it to a 
stable fuze circuit which has a known load 
curve. The desired operating point is selected 



68 


THE RADIATION INTERACTION SYSTEM 


and the output of the fuze circuit measured as a 
function of v/V. From the measured output and 
the known load curve the effective dR/R for the 
simulator can be calculated directly with no 
detailed knowledge of the diode. The theory 
above serves as a useful guide in selecting 
proper diodes and in indicating the range of use- 
fulness of a given simulator. 

The diode simulator has a considerable 
advantage over thermistor-type simulators 



because there is no delay in response to the 
applied audio voltage. Tests have shown that 
the device will follow frequencies far in excess 
of any required in fuze testing. 

Resistance Component Simulators 
(Thermistors) 

The effective resistance of an r-f circuit can 
be controlled by incorporating a thermistor ele- 
ment somewhere in the network. The temper- 
ature of the thermistor can be varied at an 
audio rate by passing audio-frequency current 
through it. This results in a variation of the 
effective resistance of the r-f circuit at an audio- 
frequency rate. 

Typical thermistors that have been used are 
small flashlight bulbs and Littel fuzes. Because 
of the thermal lag of such devices the upper 
audio frequency is quite limited, and each de- 
vice requires calibration against a standard 
fuze circuit of known stable performance. 


A detailed description of a thermistor simu- 
lator and its calibration will be found in an 
NDRC report, 3 which shows the general pro- 
cedure for calibration of any resistance simu- 
lator. 

Resistance Component Simulators (Triode) 

The effective resistance of an r-f circuit can 
be controlled within limits by loading it with 
a triode so arranged that the dynamic plate 
resistance of the triode is used as an r-f re- 
sistance. The value of the dynamic plate resist- 
ance can be changed by changing the grid to 
cathode potential of the triode. The changes in 
plate resistance respond to changes in grid 
voltage at frequencies far greater than any 
needed in fuze testing. Hence this device com- 
pares favorably with the diode simulator. Cali- 
bration is necessary, and in general the circuit 
arrangement is more complicated than for an 
equivalent diode simulator. The details of a 
typical triode simulator developed by the Philco 
Corporation are shown in their final report. 70 

Rotating Vector Simulators 

There has been little need for true rotating 
vector simulators aside from the pole test, which 
serves as a final check on any fuze circuit. In 
some special phases of fuze work, however, a 
rotating vector simulator is of interest. 

Several schemes have been proposed and two 
put into practice. One of these is a side-band 
type by Airborne Instruments Laboratory for 
use in their countermeasure studies; another 
has been designed by Westinghouse for testing 
a pulse type of fuze. 

The first type receives a carrier from the 
fuze, adds two side bands at simulated doppler 
frequency and cancels out the carrier plus the 
lower side band. The upper side band is ampli- 
fied and reradiated to form a true rotating 
vector simulator when mixed in the fuze cir- 
cuit. The details will be found in an NDRC 
report. 92 

The second type uses a transmission line with 
two resistance simulators located at points sep- 
arated by (1/8). The audio drive on one simu- 
lator is 90 degrees ahead of that on the other. 
The resultant effect of the two is a rotating 
impedance vector at the input to the line, when 



SIGNAL SIMULATION 


69 


the load presented by each simulator is prop- 
erly adjusted. 


Laboratory Audio Simulator 

As has already been pointed out the voltage 
wave into the amplifier is of the form 

dV = MS, (151) 

and S is essentially a constant of the r-f system. 


forms of M were sufficiently simple, laboratory 
sine wave oscillators could be used for all audio 
circuit tests. 

The rate of change of instantaneous fre- 
quency and amplitude of the M wave for an 
airborne target are so large that it is extremely 
tedious to predict amplifier performance on the 
basis of its steady-state response to sine waves 
of various frequencies or on the basis of its 
transient response to a unit pulse. 

It has been found very convenient to circum- 



Figure 39. Audio-frequency M- wave simulator; view of drum and associated equipment. 


The control of burst and discrimination against 
noise are performed in the amplifier control 
section of the fuze. In testing this part of the 
system, it is not necessary to include the r-f 
elements, provided an audio voltage wave pro- 
portional to M can be generated. If actual wave 


vent these difficulties by constructing an audio- 
frequency simulator which generates a wave 
which is in detail like the wave measured in the 
fly-by tests described in Section 2.11.3. 

In principle the device is quite simple. The 
desired wave form is cut on an opaque paper 


70 


THE RADIATION INTERACTION SYSTEM 


tape and wrapped around a transparent cylin- 
der. A light source is placed inside the drum. 
It illuminates a tiny transverse strip of the 
tape by means of a slit. A photocell on the out- 
side of the drum measures the light passed by 
the tape. When the drum is rotated by a motor 
drive, the M wave of voltage is generated. 

Since the form of the M wave does not de- 
pend upon the speed of the projectile, the same 



Figure 40. Audio-frequency Af-wave simulator; 
view of control panel. 


wave can be used for all projectile velocities. 
Thus the speed of rotation of the drum corre- 
sponds to projectile velocity, and a whole range 
of interaction velocities can be simulated with 
a single adjustment. 

If an oscilloscope sweep is synchronized with 
the drum rotation, it becomes a simple matter 
to investigate delay in circuit response. By in- 
corporating several channels, noise of typical 
forms can be superimposed on the M - wave sig- 
nal to demonstrate the discriminating proper- 
ties of audio control circuits. 

Figures 39, 40, and 41 show photographs of 


a typical audio simulator, and oscillograms ob- 
tained with it. 

The audio simulator is used also in studies of 
the ground-approach M wave. Although this 
wave form is not so complicated as that from 
an airborne target, the rate of rise of amplitude 



Figure 41. Simulated M wave obtained with 
audio-frequency M-wave simulator, with super- 
posed response of amplifier to simulated M wave. 

In each photograph the curve of larger ampli- 
tude represents the M wave. The superposed 
amplifier response is scaled down. In the upper 
photograph an amplifier peaking at 100 cps was 
used ; in the lower photograph the amplifier 
peak was 50 cps. 

is large enough to make dynamic studies of the 
amplifier necessary. These are performed more 
easily on the audio simulator than by calcu- 
lation. 

The audio simulator has proved itself to be 
a worth-while research tool and may be of con- 
siderable use for other laboratory work. 






ANTENNA NOISE 


71 


2.12.5 Overall Signal Simulator 

In case it is necessary to simulate at the an- 
tenna terminals the complete variation of im- 
pedance, a combination of the audio simulator 
with the resistance simulator of the diode or 
triode can be used. The voltage from the audio 
simulator is used to drive the r-f resistance sim- 
ulator. The result is a wave which presents the 
correct variation of radiation resistance to the 
fuze circuit. Reactance changes will not be in- 
cluded, but they are not normally needed. 


2 13 ANTENNA NOISE 

2 131 Introduction 

We have seen in equation (44), reproduced 
here for convenience, 10 * 42 45 that the presence of 
a reflecting body changes the input impedance 
of the fuze antenna, thus 

Z x = Z n - Z r . (44) 

We in effect altered this equation to read 



and tacitly assumed that Zu is constant so that 
the only changes in Zi are those produced by M. 
We have also seen that expected values of M 0 are 
very small (~ 0.0025 for the airborne-target 
case) and that fuzes are designed to work on 
these small changes when they have a proper 
time dependence. 

Now a fractional change in Zn will be just 
as effective in actuating the fuze as the whole 
of M, if it has the proper time dependence. Such 
a change is indistinguishable from the expected 
signal, and the fuze will function if these 
changes in Zu occur. 

There are two physical differences between 
the Af signal and a variation of Zn. These are 
(1) the time delay associated with the time of 
flight of the radiation to the target and back 
and (2) the fact that the M signal is a return- 
ing wave instead of an outgoing wave. 

Up to the present time no practical schemes 
have been evolved for making any differenti- 
ation. Such schemes will no doubt be developed, 


but the fuzes with which this report is con- 
cerned cannot make the distinction. The con- 
ventional radar pulse-time system makes the 
necessary distinction but has not yet been de- 
veloped in a form suitable for small fuzes. 
Hence a variation of Z n gives rise to a signal 
of the same form as the M signal. 

Unfortunately circumstances arise wherein 
Zn is not constant, and we are forced either 
to rely upon the difference in time variation to 
discriminate between M and variations in Z n 
by means of the audio control system or to go 
to severe lengths to hold Z X1 adequately con- 
stant. There are two sources of variation in Zu. 
These are (1) geometric deformations of the 
antenna structure associated with vibration, and 
(2) erratic additions to the antenna system 
arising from propellant flames associated with 
the projectile itself. The latter source of trouble 
is associated only with self-propelled projec- 
tiles such as rockets or guided missiles. 

It may be mentioned that the problem of 
thermal noise never arises, since the signal 
levels used are always much higher than the 
thermal noise level. 

Signals originating in radiators other than 
the fuze are considered interference, and the 
susceptibility of fuzes to these signals is not 
primarily an antenna problem but rather an 
internal circuit problem. The antenna plays a 
small part by virtue of its reception pattern, 
effective length, and polarization. These prop- 
erties have been discussed in preceding sections 
and need not be considered further. 

The whole interference problem is intimately 
related to the problem of countermeasures for 
the fuzes and is therefore not treated in detail 
here. We now turn attention to the antenna 
noise as defined above. 


2.13.2 Antenna Noise Resulting from 
Geometric Deformations 

The normal dimensional deformations asso- 
ciated with vibration in projectiles are so small 
that they can be neglected. The real trouble 
arises when the vibration varies the contact re- 
sistance (or impedance) between parts of the 
projectile. This may occur between parts of a 


72 


THE RADIATION INTERACTION SYSTEM 


welded-fin structure on bombs, at the point 
where the tins are attached either on bombs or 
rockets, at the point where the fuze is attached 
to the projectile, and at the point where the 
power vane is attached to the fuze. 

The obvious solution to the whole problem is 
to make all joints so tight electrically that the 
variations do not matter. Usually it is possible 
to achieve the required tightness provided (a) 
the fins are made properly, and (b) the assem- 
bly is tight when the projectile is used. It is 
difficult, if not impossible, to simulate in the 
laboratory vibration conditions like those set 



Figure 42. Two possible current distributions 
on fuze antenna. 


up in the actual projectile. Thus the only ex- 
perimental method of determining when the 
desired degree of tightness has been achieved 
is to make field tests with real projectiles carry- 
ing fuzes known to be internally quiet. Such 
experiments are made with each type of pro- 
jectile to be used, for “proving-in” purposes. 

The antenna noise generated by the rotating 
power vane cannot be removed by tightening 
the system. It can be reduced by putting an 
electric shield around the propeller, as in the 
case of the ring-type antenna, or by using a 
rotating system whose speed is so high that 
the noise frequency is higher than the expected 
doppler frequency. The audio control system 
can then discriminate between the doppler fre- 
quency signal and the antenna noise. This latter 
device is used in both bar- and ring-type fuzes. 
The erratic noise set up in the nose bearings is 
reduced to an acceptable level by keeping the 
amount of metal in the rotating system exposed 
to r-f fields very small. 

When tactical conditions and engineering de- 
sign considerations permit, the noise level can 
be reduced by an appropriate choice of carrier 
frequency. To see this consider the schematic 


antenna system shown in Figure 42. The dif- 
ferent standing waves of current are shown by 
the dotted lines. The single-lobe pattern corre- 
sponds to a frequency such that the antenna 
is about (A/2) long. The double-lobed pattern is 
that for a frequency such that the antenna 
is nearly l long. Suppose that the contact re- 
sistance varies at point x. The current through 
x is larger for the l wave than for the {1/2) 
wave. Hence the power absorbed at x varies 
more for a given variation in x when the l pat- 
tern is used than when the (A/2) pattern is 
used. Power absorption appears as variations in 
Z ? i and hence appears as a spurious signal. 

If the noise point happened to be at y, the 
l pattern would be better. Usually the fuze 
joint is near one end and the fin joint near the 
other, and it is not possible to get a current 
pattern which places nodes at these points. 
Furthermore, fat antennas do not have marked 
nodes except at the ends. For this reason it is 
generally better to use a low carrier frequency 
to suppress vibration noise. 

This argument has been verified in the field 
in the case of longitudinally excited 500-lb 
bombs. 


2.13.3 Antenna Noise Resulting from 
Propellant Flames 

Rockets are particularly subject to this type 
of noise, since they carry a long flame behind 
them for a considerable portion of their flight. 
It is possible to delay the arming of the fuze 
until the propulsion blast is over without im- 
pairing the effective use of present-day rockets 
too greatly. However, the trend is toward longer 
burning rockets and the flame is sure to become 
a serious problem. Furthermore, there is more 
to the problem than first appears. When the 
burning is over, the flame does not go com- 
pletely out and remain so. Scraps of unburned 
propellant left in the hot motor reignite and 
give small “chuffs” of flame which do not dis- 
turb the motion of the rocket but which do 
disturb the behavior of the antenna. These 
chuffs of flame have been found to occur er- 
ratically many seconds after the main burning 


SECRET 


ANTENNA NOISE 


73 


of the propellant has ceased. They create large 
enough changes in Z X1 to cause the fuze to func- 
tion before it reaches its intended target. The 
problem of afterburning, as the phenomenon of 
the chuffs has been called, has been a serious 
one in the case of present-day rockets, and con- 
siderable effort has been expended in seeking 
a solution of the problem. 

The attack on the problem has taken two 
main lines. These are as follows: 

1. A study of the electric properties of the 
flames to see how circuits can be designed to 
suppress the response. Such electric properties 
are within the scope of this chapter. 

2. A study of the means for eliminating the 
afterburning problem by stopping the after- 
burning. This phase of the attack is treated in 
another chapter, since it is not an antenna 
problem. 

The electrical effects of the flame result in 
the production of a spurious signal which can 
be distinguished from the expected M signal 
only by its different time variation. It has been 
a simple matter to show that the flame does 
actually produce large spurious signals. A 
rocket carrying a fuze was mounted on an in- 
sulating stand and connected through insulat- 
ing hose to supplies of gas and air. By this 
means flames of any desired size could be pro- 
duced at the end of the projectile. Recording 
instruments were connected to the fuze in such 
a manner as to leave its radiating properties 
essentially undisturbed. 

Arrangements were also incorporated so that 
the flames could be started or stopped quickly. 
The sudden change gives rise to time-dependent 
effects which can be easily separated from the 
steady-state r-f conditions in the absence of 
the flame. Several interesting properties of the 
flames were immediately evident. 

1. The yellow sooty flames from pure illumi- 
nating gas had no measurable effect. 

2. The clear blue flame from a mixture of 
gas and air had no effect. 

3. When arrangements were made to spray 
NaCl, or KC1 solution or powdered salt into the 
flame, a large response was observed immedi- 
ately. The changes were five to ten times those 
needed to trigger the fuze normally. 

4. The effective flames were not in contact 


with the fuze, being separated from it by an 
inch or more of nonburning nonionized gas. 

5. The magnitude of the effect could be 
changed by changing the concentration of the 
ionizing substance injected into the flame. 

6. The magnitude of the effect could be 
changed by changing the flame length. 

Figure 43 shows a typical curve of signal 
versus flame length. The ordinate is expressed 
in terms of the value of M 0 that would be re- 
quired to give the same signal. The arrow near 
the base at 0.0025 represents the working value 
of M 0 for which the fuze was designed to fire 
when the proper signal is approached. 

It was next necessary to demonstrate that 
the rocket propellant actually carried enough 



0 10 20 30 

FLAME LENGTH (INCHES) 


Figure 43. Signal produced by flame, as func- 
tion of flame length. 

ionization to d,o what the flames did. To check 
this a rocket was supported on a strong insu- 
lating support, and voltage changes measured 
while the main burning was going on. Voltages 
larger than in the above described experiment 
but of the same order of magnitude were ob- 
served. The effect of afterburning was checked 
by putting small amounts of propellant near 
the nozzle of the motor and igniting them with 
a hot wire. The signals from the lower-temper- 
ature burning were still of the same order of 
magnitude. 

These tests leave no room for doubt about the 
signal-producing properties of a flame. Field 


SECRE' 


74 


THE RADIATION INTERACTION SYSTEM 


tests have shown that such flames do exist and 
that they are associated with fuze functions. 

Studies of circuit behavior were undertaken 
to see if other carrier frequencies might be use- 
ful. Reasonable changes which could be readily 
incorporated into the fuze design were investi- 



Figure 44. Diode voltage versus antenna length. 


gated. None of these changes eliminated the 
effect of the flames. 

Figure 44 shows curves of the d-c voltage 
output (diode voltage in this case), from the 
r-f section as a function of the length of the 
projectile-antenna. Time-dependent changes in 
this voltage represent the dV set up by the 
M wave. In effect the curve may be considered 
to be a plot of R v although it is not exactly pro- 
portional to it. 

To get the curves a piece of brass pipe was 
used to simulate the rocket. The upper dotted 
curve in this figure shows the voltage as a func- 
tion of the length of brass pipe. The length of 
33 V 2 in. corresponds to the length of the rocket 
for which the fuze was designed. 

The lower two curves show the response when 
the length in excess of 33!/£ in. consisted of a 


paper tube coated with Aquadag. The coating 
was found to have a d-c resistance of 20 ohms 
per in. for the upper curve and about 100 ohms 
per in. for the lower curve. These curves indicate 
the effect of an extension to the antenna which 
is not a very good conductor. That is, it simu- 
lates more nearly the conditions of the conduct- 
ing flame. We see that the lengthening of the 
antenna gives voltages which are very large 
compared with the 30-mv signal required to fire 
a fuze. They are larger than those observed 
from the flames. This was thought to be due 
partly to the air gap between the flame and the 
antenna. 

To show that the size of the gap makes a 
considerable difference in the effect of the ex- 
tension, two cases of metal extensions were 



SEPARATION (INCHES) 


Figure 45. Effect upon diode voltage of metal 
extensions to antenna. 


investigated. Figure 45 shows the results. A 
12-in. length of pipe changes the voltage about 
10 v when connected directly to the end of the 
antenna. When pipe and antenna are separated 
to leave a i^-in. air gap the effect is reduced to 
about 1 v, the order of magnitude of the meas- 
ured effect from the flames. If a resonant length 
of pipe is used for an extension, the effect is 
not so sensitive to separation. Still there is a 


SECRET 


EVALUATION OF C 


75 


marked reduction for an inch separation, which 
is about the space observed between the flame 
and the projectile. There is, of course, no way 
of knowing what the length of a particular flame 
may be from any particular projectile. All we 
can say from these experiments is that the 
effect of flames is consistent with a theory of 
antenna length changes. 

We see from the figures that it is possible for 
a change in antenna length either to increase 
or to decrease the voltage by selecting the fre- 
quency or length properly. In particular, for 



Figure 46. Horizontal differential antenna with 
its image. 


one assigned length of extension, there is a fre- 
quency for which the voltage change due to the 
presence of the extension will be zero. 

In the course of field tests on the afterburn- 
ing problem, fuzes, operating above and below 
the resonant frequency, were tried to see if the 
effect of the flame could be reduced. No im- 
provement resulted, presumably because (1) 
the flame lengths were too variable, or (2) the 
transient setup by its change of length or posi- 
tion was too great. 

The discussion of the response to flames has 
so far been concerned with the magnitude of 
the effect. There remains the problem of its 
time dependence. If the changes of Z X1 set up 
by the afterburning flame have the same time 
dependence as the expected signal, no internal 
circuit can discriminate against it. (This as- 
sumes the use of a load-sensitive r-f system.) 

To date it has been impossible to learn much 
about the wave form of the afterburning signal. 
Static measurements leave out the large effects 


of the airstream on the flame behavior and 
hence give only crude qualitative answers. 

Some investigations have been made to see 
if a change in the frequency response of the 
audio-frequency control circuit would reduce 
the response to afterburning. No significant 
results were observed. This probably means 
that the actual afterburning wave form is so 
erratic that it has sizable components in the 
pass band of an otherwise acceptable control 
circuit. 

Real improvement has, however, been made 
in reducing the afterburning effect by chang- 
ing the design of the propellant or the motor 
or both. 10 These are temporary expedients, since 
it is unwise to have the fuze properties dictate 
propellant and motor design. 

There are definite lines of attack which indi- 
cate that the response to afterburning and even 
main burning may be reduced to a negligible 
value by changing the basic design of the fuze. 
However, a discussion of such changes is be- 
yond the scope of this volume. 


2 14 EVALUATION OF C 

This section 23 * 24 and the following contain 
additional material supplementing some of the 
discussions in the preceding section. 

In Section 2.4 two relations were derived 
which are here repeated for convenience. 


V(Z oR.G/4*) mt) 

Zl3 = -^^\/RsiRssGiG 3 fi(dn,<f>i3) f 3 ( 631 , (j)3i). 

(cos r)je -2,rr/x) . (42) 

It has been shown that C is a constant for all 
antennas. The evaluation of C allows the com- 
pletion of the general equation (42) for the 
mutual impedance between any two antennas 
(only radiation fields considered). 

Since C is a constant, we are justified in 
choosing the simplest possible antenna in the 
evaluation of C. The antenna chosen is the 
infinitesimal or differential antenna. For such 
an antenna, f(6,<\>) = sin 6 and G = %. The 
current, whose absolute value will be called 7 0 , 



76 


THE RADIATION INTERACTION SYSTEM 


is constant over the infinitesimal length of the 
antenna. The power W radiated is 

W = ^£. (153) 

Any change A R s in the radiation resistance is 
accompanied by a char ge A IF in the power radi- 
ated, given by 


current 7 0 in No. 1 constant in the presence of 
No. 2, we in effect cancel out the scattered wave 
from No. 1, since the scattered wave results 
from an additional current in No. 1. Thus we 
need consider only the direct contributions from 
No. 1 and No. 2 . At any point P on the hemis- 
phere S, whose radius is R (Figure 46), the in- 
stantaneous electric field due to No. 1 is 


AW = 


I o 2 A R, 


(154) 


Ei = sin 6 e&* ™ *)]. ( 155 ) 

K 


The above expression is based on the assump- 
tion that the current remains constant. 

These relations will be used in evaluating C. 
We shall obtain the mutual impedance between 
an infinitesimal antenna and its image in the 
following manner. First we shall compute the 
additional power AW, which the antenna has 
to radiate to maintain its current 7 0 constant 
in the presence of the image. Then, utilizing 
equation (154), we shall obtain the resistance 
component of the mutual impedance. Finally, 
with the aid of equation (42) C will be found. 

Consider the differential antenna to be placed 
horizontally at a height h above an infinite 
perfectly conducting horizontal ground (Fig- 
ure 46) . The antenna and its image, to be called 
respectively No. 1 and No. 2 , form a system 
of two interacting antennas. For this system 
fi(0i2f<t>i2) — f 2(^21, 4>2i) — 1> and cos t = 1. 

We now have to compute the additional power 
radiated by the antenna to maintain its free- 
space current 7 0 in the presence of the ground 
or image. At this point one advantage of using 
the infinitesimal antenna in this calculation 
may be mentioned. It is only for such an an- 
tenna that we can be sure that the free-space 
current distribution can be maintained in the 
presence of the ground. 

To find AW we can integrate the Poynting 
vector over a sphere S of large radius. This 
gives us the total power ; subtracting the free- 
space power W 0 , we obtain AW. 

The fields along the surface of the sphere are 
due to contributions from the real antenna and 
its image. In general, some of the radiation 
from the image (antenna No. 2 ) is scattered 
by the real antenna, No. 1. The effect of No. 2 
over the surface S is the sum of radiation from 
No. 2 plus scattering from No. 1. By holding the 


The field due to No. 2 is 


Ez = — ^ sin 8 e&* -<*<*+'“ *». 

R 

In equations (155) and (156) 

7 _ \ZqRsG 
k - 


(156) 


\[/ = the angle which the radius vector R 
makes with the vertical (Figure 46). 

/3 = 27r/X. 


The other symbols have been previously defined. 
Inequations (155) and (156) the induction and 
quasi-static fields have been ignored, since they 
do not contribute to the power radiated. Adding, 
we have 


E = E\ -(- E2 

= ^ sin 6 e^ 031 
n 


- PR) 


jgi/3/i cos t _ e - jph cos (157) 


To find the total power W, we have to integrate 
\E\ 2 /Z 0 over the hemisphere. The details of the 
integration will be omitted. The result is 


w 47r/o 2 /c 2 , 7r7 o 2 k 2 
W = —^7? 1 ~ — • 




3Z 0 
sin 2 (3h 


2 W 


cos 2 j Qh + 


4 m 


The free-space power W 0 is 
4 tt7 0 2 fc 2 


Wo = 


3Z ( 


3 sin 2/3/i J. 

(158) 

(159) 


Therefore, 


I F — IF 0 A IF AR S _ 

W 0 Wo R s 

1 [w sin m ~ 2<m cos 2/3/1 + w sin wh ] 

(160) 


PATTERN ERRORS DUE TO GROUND REFLECTION 


77 


It will be noted that as h approaches zero 
(A R s /R s ) approaches —1, showing that the an- 
tenna does not radiate when on the ground, as 
is known. 

If h be selected large enough so that the 
inverse square and cube terms in h may be neg- 
lected, we have 


AR S 3X . Mi 

R s ~ 8irh Sm X ' 


(161) 


Thus we see that under such conditions the re- 
sistive component of the reflected impedance is 
proportional to R s and varies harmonically with 
the separation between antennas (results ob- 
tained previously by other means). With the 
aid of equation (42), it is now seen that 


(2) a reflected ray from the ground. It is con- 
venient in computing these effects to treat the 
radiating system as consisting of the transmit- 
ting antenna and its image. 

In Figure 47 the coordinate system is a rec- 
tangular xyz system with origin at the center 
of the image antenna; the image antenna lies 
along the y- axis. The real antenna is situated 
at a height z = 2h above the xy plane. The 
receiving dipole is at a distance a from the 
transmitter and is always tangent to a circle 
of radius a whose center is the transmitter. 
The angle 6 is the angle of azimuth and repre- 
sents the angle of rotation of the antenna in 
the field setup. The angle of elevation of the 


CZp „ r _ 3A „ 

8t rh ~ 8t rh 8 


Since G = •%, we obtain 


(162) 


C = 9?. (163) 

It is also interesting to note that this calcu- 
lation, which is based upon radiation fields 
alone, shows the contribution to the radiation 
resistance arising from the interaction between 
inverse square and inverse cube fields of an- 
tenna and image, which of themselves do not 
radiate power on the average. 23 ’ 24 While this 
argument holds for the infinitesimal dipole, it 
does not hold for large antennas, since the prox- 
imity to ground may alter the current distribu- 
tion on the finite antenna. The argument gives 
correct results for distances large compared to 
the dimensions of the antenna. 


2.i5 PATTERN ERRORS DUE TO 
GROUND REFLECTION 

The experimental setup for measuring direc- 
tivity patterns has been described in Section 
2.8. There are certain errors inherent in these 
measurements because of the reflection from 
the ground ; it is the purpose of this section to 
discuss these errors. 

Referring to the field setup described in Sec- 
tion 2.8, the resultant field strength at the re- 
ceiving antenna is composed of two parts : (1) a 
direct ray from the transmitting antenna, and 



Figure 47. Coordinate system used for com- 
puting reflected field in radiation pattern setup. 


dipole with respect to the image antenna is a. 
The distance from the image to the dipole is r. 
It is seen that cos a = (a/r). 

The ray from the real antenna to the dipole 
makes the angle 6 with the axis of the antenna 
and is perpendicular to the dipole. The electric 
vector associated with this ray is parallel to 
the dipole. The ray from the image to the dipole 
is also perpendicular to the dipole and makes 
an angle y with the image. The term y, as shown 
in the diagram, is given by the relation 

a cos 6 

cos y = — - — = cos a cos 6. (164) 

From the relation of equation (164) , y is plotted 
versus 6 (Figure 48) for a = 15 degrees, which 
represents the actual situation for the measure- 
ment of a large number of patterns. Now the 
electric vector associated with the reflected ray 


SECR 


78 


THE RADIATION INTERACTION SYSTEM 


is not in general parallel to the dipole. The com- 
ponent E r of the electric vector of the reflected 
ray, parallel to the dipole is given by 

E r = E( 7 ) cos r. (165) 

In the above equation E ( y) represents the radi- 
ation field in the direction y from the image 
antenna. The term t is the angle between the 
direction of E( y) and the dipole. The term 
E( y) is in the plane determined by r and the y 
axis, and is perpendicular to r. 

Then t may be evaluated as follows : The di- 
rection cosines l, m, and n, of the dipole are seen 
from Figure 47 to be 

l = cos 6 , 
m = sin d, 
n = 0. 


For the direction of E( y) we obtain the corre- 
sponding values : 

_ a sin 6 _ cos a sin 6 
r tan y tan 7 ; 


m = sin 7. 


Then 


cos 0 cos a sin 0 . . _ . 

cos r = + sin 0 sin 7, 

tan 7 


cos 7 sin 0 
tan 7 

sin 0 
sin 7* 


+ sin 0 sin 7, 


Thus we have 


E r = E{ 7) 

sin 7 


(166) 


The correction factor (sin 0/sin y) = cos t is 
plotted versus 0 in Figure 48 for y = 15 de- 
grees. 

The total field strength parallel to the receiver 
is the resultant of E r and the field associated 
with the direct ray, denoted by E d . This re- 
sultant we shall call E r 

We may write E d and E r as follows : 


E d 


4M ei m 


- (3a -e ( 0 )] 

> 


(167) 


E r = 
Also 


nAf(y} sin 8 ^ _ * _ <w _ „ 
r sin 7 


(168) 


E t = E d + E r . (169) 

In the above equations, A is a constant of 


proportionality, and f( 0 ) and / (y) are the 
magnitudes in the true radiation pattern for 
6 and y; the terms e( 0 ) and e(y) represent 
the phase of the radiation field for 0 and y; 
a and r are the distances from the receiving 
dipole to the fuze antenna and to its image 
respectively ; n is the magnitude of the 



Figure 48. 7 and cos r versus 6 . 

reflection coefficient, appropriate to the type 
of ground under consideration ; $ is the 
phase angle associated with this reflection ; 
P= (2:tA). 

The image representation used here does not 
fully represent the changes in polarization oc- 
curring at reflection when n 7 ^ 1. An examina- 
tion of the geometry shows that the receiver 
dipole responds only to the component of the 
electric field that is parallel to the ground at 
reflection. The vertical component whose ab- 
sorption is most sensitive to ground properties 
is ignored. Thus we may safely use the image 
representation with an effective reflection co- 
efficient n. It may be noted also that this coeffi- 
cient is a constant for all angles 6 of the trans- 
mitter, since the angle of reflection to the re- 
ceiver is not altered. 

A square law detector is used, so that the 


SECRET 


79 


PATTERN ERRORS DUE TO GROUND REFLECTION 


measured directivity pattern, when normalized 
to unity, is given by 

\E t (e) [ 2 

I ’max’ 

where |Z^| max is the maximum value of | E t \. 
What is desired, however, is the true pattern 
given by 


\Me) | 

\E 


-Pie). 


Now n/r may be written as N/a, where N, as 



Figure 49. f(d) and f(y) cos r for electrically 
long antenna. 


where A' is a new constant of proportionality. 
Thus 

jf#n - ™ 

where q is the expression in brackets in equa- 
tion (171). 

When the fuze antenna has the pattern of an 
elementary dipole, we have 



e° 

Figure 50. Typical theoretical pattern / 2 (0), 
with per cent error due to ground reflection. 


thus defined, differs in general by a few per 
cent from n. We may then write 


E t {6) = — e j[ut - & a - «(*)]. 


sin 


f(6) + NfM e’T* W + £ W1 
sin 7 


}, 


where we have defined 

$i = —(3(r — a) — 4>. 


(170) 


Then 

\E t {e)V = A’ [ 


m + N^y) 8 ^ 


+. mw(y) gjpj cos (*, + €(«) 




c(t) 
(171) 


which makes 


f(y) ^ = m. (174) 

sin 7 v J 

Furthermore, there is no phase dependence on 
6 ; that is 



t{6) — e(v) = 0 . 

(175) 

Then 




q = S\d) [1 + N* + 2N cos $J, 

(176) 

so that 




\E t m . m rfn) 

1 Ei | 2 m ax " PWrr** 3 W ‘ 

(177) 


Thus for this limiting case, the errors reduce 
to zero. 


SECRET 




80 


THE RADIATION INTERACTION SYSTEM 


We have seen that when the conditions of 
equations (174) and (175) hold the errors re- 
duce to zero. In practice, for the fuze antennas 
in use, these two conditions are so nearly ful- 
filled that the errors are small. Figure 49 is an 
example of how nearly equation (174) is ful- 
filled, even in the case of complicated patterns. 
The solid line represents a three-lobed pattern 
f(6) obtained with an electrically long projec- 
tile. Although this is an observed pattern, it 
represents a possible true pattern. The crosses 
are the values of /(y) cos t obtained by utilizing 
the relations in Figure 48. For simpler patterns 
the differences between f{6) and /( y) cos t are 
less than those in Figure 49. 

It was mentioned in Section 2.8.2 that the- 
oretical patterns representing very good fits for 
the observed patterns may be obtained by as- 
suming a current distribution of the form 
shown in equation (98). Such computations 
afford a means of estimating e(<9) — e(y) and 


also /( y) cos x. Such calculations over a range 
of conditions indicate that s (0) — e(y) does 
not exceed 5 degrees for patterns now in use. By 
using the values thus found and combining 
them with a range of assumed values for 4>, 
and n, values of q/q max may be computed. Such 
computations lead to the conclusion that the 
error from those sources will rarely be in excess 
of 5 per cent. 

Figure 50 is an illustration of the extent of 
the errors found by such considerations. The 
solid line represents the / 2 (<9) calculated from 
the type of current distribution mentioned, with 
R and 5 chosen to give a typical bomb radiation 
pattern. The dashed curve represents the per- 
centage of error obtained by assuming <I> = 
(jt/2), n = 1, values which give approximately 
maximum errors. The percentage of error curve 
is a plot of 

™[ q/rm m m ] versus e - 


Chapter 3 

ELECTRONIC CONTROL SYSTEMS 5 


T he basic physical phenomena underlying 
the production of an actuating signal for a 
doppler-type radio fuze have been discussed. 
This chapter is concerned with the problems 
of designing electric circuits to convert the 
signal so that a missile will be detonated in 
accordance with the military requirements. In 
the preceding chapter it was shown that the 
interaction between a radiating system and a 
reflecting target can be considered as a load 
variation across the two terminals connecting 
the antenna with the oscillator. The variations 
in load occur at an audio rate. The problem of 
this chapter is to show how the variations in 
antenna load are converted to a signal which 
will detonate the missile at the proper point on 
its trajectory. 

There are five major subdivisions in this 
chapter : 

1. The r-f section which treats of the design 
of oscillator detector circuits which respond 
properly to variations in loading. 

2. The audio-frequency section which dis- 
cusses methods of controlling the load-variation 
signal so that it will reach the proper amplitude 
at the proper time. 

3. The detonator section in which it is shown 
how an audio signal of requisite amplitude ini- 
tiates an explosive train. 

4. The power supply section in which ways 
and means of supplying electric energy to the 
electronic circuits are described. 

5. A coordination section in which the vari- 
ous design compromises are discussed. 


31 RADIO-FREQUENCY SYSTEMS* 

311 General Requirements of the R-F Unit 

The r-f system was originally conceived as 

a This chapter, which consists of five major sections, 
was prepared by several different authors. They are 
named in footnotes to the headings of the various 
sections. 

b This section was prepared by Chester H. Page, of 
the Ordnance Development Division of the National 
Bureau of Standards. 


a combined transmitter-receiver, converting the 
target-approach doppler frequency into an 
audio-frequency signal by rectification. The cir- 
cuit engineering is simplified by viewing the 
net electromagnetic behavior of the radiating 
missile as a two-terminal variable impedance. 
For practical purposes, it is sufficient to con- 
sider this impedance as the parallel combina- 
tion of a constant reactance and a variable 
radiation resistance. The fixed reactance branch 
can be mentally combined with the transmitter 
circuit, simplifying the problem to that of an 
oscillator feeding a variable resistance load. 

The net radiation resistance load is a func- 
tion of fuze and missile dimensions as well as 
operating frequency. The fuze and missile com- 
binations in use lead to radiation loads ranging 
from 1,500 to 150,000 ohms, a total range of 
two decades. In general, the low end of this 
range is associated with long missiles, such as 
the larger rockets and bombs; the medium 
range (up to 20,000 ohms) is associated with 
medium size bombs ; and the upper range with 
the small mortar shells. The extreme case of 

150.000 ohms is contributed by the fuzes using 
transverse-dipole or loop antennas. The small 
mortars present radiation resistances from 

6.000 to 100,000 ohms, by virtue of the extreme 
frequency range used. 

The most severe aspect of the large load 
range is its effect on the design of a “universal” 
fuze. A fuze designed for interchangeable use 
on all bombs must operate satisfactorily over 
at least a tenfold range of values of load re- 
sistance. When the use of a fuze is limited to 
a specific missile, the circuits can be designed 
for the optimum match between source imped- 
ance and load. The goal of semiuniversality, to 
reduce the required number of models, places 
a severe limitation on the types of r-f systems 
that can be employed. 

The most elementary r-f system for a prox- 
imity fuze consists of a low-power oscillator, 
relatively heavily loaded. This may be consid- 
ered to be an “oscillating detector” and is oper- 
ated under approximately the same condition 



81 


82 


ELECTRONIC CONTROL SYSTEMS 


as utilized for autodyne reception of telegraphic 
communications. The basic design consists of 
an oscillator with little regeneration, operating 
under Class A grid conditions, developing its 
own grid bias across a large grid leak resistor 
(of the order of a megohm). The plate current 
is supplied through a resistor of some 50,000 
ohms. The coupling between the oscillator and 
antenna is sufficiently tight to place the oscil- 
lator on the verge of instability from overload. 
Under these conditions the plate current (and 
therefore the plate potential also) is a sensitive 
function of load resistance. Such a scheme al- 
lows the conversion of radiation resistance 
variation into an audio signal appearing across 
the triode plate circuit resistor. The funda- 
mental weakness of this circuit arrangement 
lies in the small range of radiation load for 
satisfactory operation. This precludes its use in 
semi-universal fuzes, and also leads to critical 
load coupling adjustment. Little attention has 
been paid to this type of circuit. 

Another circuit based on the concept of sep- 
arate functions of transmission and reception 
used a stable power oscillator inductively 
coupled to the antenna circuit. A tuned diode 
detector was also coupled to the antenna circuit 
for rectification of the doppler frequency 
beats. Very early in the program, it was 
realized that the transmission-reception-detec- 
tion problem could be considered as a vari- 
able antenna resistance problem, as previously 
discussed. This realization led to a simplifica- 
tion of the circuit, by combining the tuned diode 
circuit and antenna coupling functions. The 
new arrangement comprised a tuned diode volt- 
meter across the antenna terminals, with the 
diode-antenna tuning coil inductively coupled 
to a stable oscillator operated at full power. 
This arrangement required an adjustable ver- 
nier tuning capacitance for individually res- 
onating the diode-antenna circuit to the par- 
ticular oscillator assembly. Aside from produc- 
tion problems and effects of aging on the tuned 
circuit, this design leads to difficulty for semi- 
universal application by virtue of the different 
antenna reactance presented by different mis- 
siles. Although this reactance variation for one 
family of missiles is not large, it is sufficient to 
produce appreciable detuning of the sharply 
resonant diode circuit. 


A further simplification of the fuze was based 
on the dependence of grid voltage of an oscil- 
lator on its load. Details of a practicable circuit 
were worked out in cooperation with Andrew 
Stratton of the British Ministry of Aircraft 
Production during an extended visit to the 
National Bureau of Standards [NBS]. 79 ’ 88 If 
the oscillator is operated under appropriate 
conditions of grid current and grid bias, its 
plate current is insensitive to load, but its grid 
bias exhibits a smooth reproducible dependence 
on load. This is, of course, a variable efficiency 
oscillator. The bias developed is almost exactly 
proportional to the voltage developed across the 
antenna. The antenna is tightly coupled to 
the oscillator, and the lack of sharply resonant 
coupling circuits makes the system insensitive 
to small antenna reactance differences. For the 
same reasons, operation is not sensitive to fre- 
quency differences among individual oscillators, 
and no vernier tuning adjustment need be made. 
This so-called reaction grid detector [RGD] 
circuit was used in all the later models of prox- 
imity fuzes developed by Division 4. 

A second type of oscillator reaction which 
can accommodate a wide load range was devel- 
oped and employed by the Westinghouse Elec- 
tric Corporation. 111 - 205) 206 This circuit is super- 
ficially the original oscillating detector with 
the plate resistor replaced by the primary 
winding of an audio transformer. It differs in 
the operating conditions of the triode. The 
plate current and generated power are consid- 
erably higher than in the oscillating detector, 
but the variation of plate current with load is 
still employed as the signal generating means. 
This circuit is referred to as the power oscillat- 
ing detector [POD]. The signal voltage gen- 
erated by the load resistance variation is the 
equivalent plate circuit voltage which would 
produce the observed current variations through 
the transformer impedance and triode plate re- 
sistance. The grid operates under Class A con- 
ditions, instead of the heavy Class C condition 
utilized in the RGD circuit. 

3,1,2 Sensitivity 

Definition of Sensitivity 

One fuze will be called more sensitive than 
another fuze if it will function further from 


SECRET 


RADIO-FREQUENCY SYSTEMS 


83 


the target, all conditions of use being the same. 
This is a purely qualitative concept, which can 
be made quantitative in various ways. For ex- 
ample, the “Michigan sensitivity” (see Section 
2.11) of a fuze is the theoretical function height 
over a perfect reflector of infinite extent with 
the missile approaching the target plane in the 
most favorable aspect and with the speed ap- 
propriate to the most favorable doppler fre- 
quency (audio-amplifier response). The func- 
tion height under practical conditions is pre- 
dictable from the Michigan sensitivity by ratio 
computations. This definition is still too gen- 
eral for our needs. What is desired is an ab- 
solute definition of the sensitivity of the oscil- 
lator to radiation load changes as shown in 
Section 2.7. This relates a given physical situ- 
ation to the audio signal voltage produced by 
the oscillator system. The knowledge of this 
voltage, together with the known characteris- 
tics of the amplifier and thyratron, allow the 
prediction of function heights in a straightfor- 
ward manner as shown in Section 2.9. The r-f 
system acts as a means of converting a physical 
electromagnetic situation into an electric cir- 
cuit problem. In this work, the unqualified term 
“sensitivity” has been restricted to the sensi- 
tivity of this converter and has been defined as 
the developed signal voltage divided by the frac- 
tional change of load resistance resulting in 
this signal 7 [equation (84) of Chapter 2]. Math- 
ematically it is defined for infinitesimal load 
changes and is the derivative of the operating 
voltage whose changes become the audio signal, 
thus: 


dV 

dR/R' 


( 1 ) 


Since V is the voltage (grid bias or diode out- 
put) at the operating point, and dR/R is di- 
mensionless, the sensitivity is expressed in 
volts. Rewritten in the following form it is the 
same as equation (84) in Chapter 2. 


S = 


dV 

d In R’ 


( 2 ) 


where In R refers to the natural logarithm. This 
form of the definition is more useful, since it 
shows the sensitivity of the oscillator to be the 
slope of its “load curve” plotted on natural 
semilog paper. 


We are concerned here primarily with sensi- 
tivity due to load resistance changes rather than 
load reactance changes. The possible effects of 
the latter are discussed in Section 3.1. 

It has been found that properly designed 
oscillator-diode [OD], RGD, and POD systems 
behave like ideal generators of fixed internal 
resistance, with the d-c operating voltage pro- 
portional to the load voltage. 111 This idealized 
r-f unit is quite amenable to mathematical 
analysis, and some interesting general relation- 
ships are derivable. 

Let us consider the behavior of a constant- 
current generator with internal (shunt) re- 
sistance R i and unloaded terminal voltage F «. 
The terminal voltage for any load is propor- 



Figure 1. Circuit with constant current gen- 
erator and shunt load. 


tional to the net resistance of the load and R i 
in parallel (see Figure 1). Hence, operation 
under load R yields the voltage 


y _ V co RRj _ y R 

Ri R -\- Ri R Ri 


( 3 ) 


The sensitivity may be found from equation (1) 


S = R 


dV 

dR 


= Fc 


RRi 

(R + Ri ) 2 



= Foo P (1 - P ), (4) 

where p is the “loading ratio,” or the ratio of 
loaded (operating) voltage to unloaded voltage. 

The term V is, of course, the operating volt- 
age under radiating conditions, and V m the 
voltage when the fuze is properly shielded so 
that the oscillator does not radiate. 

The final form of equation (4) shows that 
loading to one-half the unloaded voltage yields 
the maximum sensitivity for a given oscillator 
but that this adjustment is not critical (see 
Figure 2). This loading ratio is also the condi- 
tion of maximum radiated power, or the con- 


SECRET 


84 


ELECTRONIC CONTROL SYSTEMS 


dition of matching the load to the internal 
resistance. The problems involved in obtaining 
this match by the use of an impedance trans- 
forming network between oscillator and an- 
tenna will be discussed later. 

A load curve (a plot of operating voltage 



Figure 2. Variation of sensitivity S with load- 
ing ratio p. 


versus the logarithm of the load resistance) for 
the ideal generator is shown in Figure 3. It is 
seen to be a symmetrical S curve. For purposes 
of comparing actual generator performance 
with this ideal characteristic, such a curve is 
not convenient. The ideal case can, however, be 
expressed as a linear relation, allowing easy 
evaluation of experimental data. This form is 
derived from equation (3) by algebraic manip- 
ulation and is 


so that a plot of 1/V versus 1/R is a straight 
line whose intercepts are 1/Fooand — 1 /R { . This 
form is exceedingly convenient for smoothing 
experimental data and for determining the in- 
ternal resistance (R f ) of an oscillator. 

This representation of ideal generator be- 
havior allows easy comparison of actual per- 
formance data with the idealization. Good RGD 
oscillators follow this relation quite well over 
the load range for which their plate current is 
constant. If the feedback in the oscillator is not 
optimum, the plate current will vary with load. 
It has been found that in this case IJV is a 
linear function of 1/R. Since the grid bias is 
normally obtained across a grid resistor with 
ground return, it is proportional to grid cur- 


rent, and the above relations would have the 
same form expressed in terms of grid current 
instead of grid bias. In the special case where 
the grid resistor is returned to an initial bias, 
usually positive, the grid bias and grid current 
are no longer proportional, but are linearly re- 
lated. Equation (5) is then no longer valid. A 
plot of Ip/Vg versus 1/R is concave upward 
(for positive initial bias), while a plot of I p /I g 
is concave downward. A straight line is yielded 
by plotting I p /y/I g V g versus 1/R. 

For the normal grid resistor connection, the 
result that I p /V g is a linear function of 1/R 
can be directly interpreted to mean that the 
oscillator is a current generator of fixed in- 
ternal resistance whose current is proportional 
to the triode plate current. The results of the 
more complicated case where an initial bias is 
used imply that the proportionality between 



Figure 3. Loading curve for ideal generator. 


grid bias and the fictitious terminal voltage is 
not the basic relation but that the general phe- 
nomenon is proportionality between grid power 
and the square of the terminal voltage. This 
covers all the above cases. 

These relationships, equation (5) and modi- 
fications, are not directly applicable to the POD 
oscillator, where the variation of plate current 
with load is the signal generating means. Ex- 
amination of experimental data for this sys- 
tem 111 showed the plate current I p to be a linear 
function of 1/R over the load range of interest 
(see Figure 4). The equivalent signal voltage 
in the plate circuit is readily computable from 


RADIO-FREQUENCY SYSTEMS 


85 


the total plate circuit resistance, so that the 
effect of the transformer primary impedance 
at any audio signal frequency can be easily 
taken into account. These results are mathe- 
matically expressed as 


I = Io o + ^ 



The justification for replacing R p I by the 
supply voltage E n in the last step is experi- 



Figure 4. Loading curve (for POD generator) 
plotted against reciprocal load. Relation over 
range of interest (i.e., resistance values above 
100,000 ohms) is linear. For lower resistance 
values, solid line represents actual values, 
dashed line represents ideal linear extension. 


mental. Measurements of I m versus E B on pro- 
duction assemblies showed that the dynamic 
plate resistance R p was equal to the static plate 
resistance ( E B /I oo) under the operating condi- 
tions of this oscillator. 

The direct practical application of all the 
above sensitivity formulas is limited by the fact 
that the radiation resistance is not a free vari- 
able. If it were, it could be chosen to match the 
source resistance, and maximum sensitivity and 
power radiation would be obtained. The oscil- 
lator design problem would then essentially re- 
duce to the problem of designing for maximum 
grid bias under no load. 


The radiation resistance of transverse anten- 
nas is restricted to high values by the small 
dimensions involved. On the other hand, the 
radiation resistance of longitudinally excited 
antennas is adjustable through a considerable 
range of values by variation of the size of the 
exciting end cap. Unfortunately, for a given 
overall fuze length, increasing the length of the 
end cap involves decreasing the separation be- 
tween the end cap and the missile. (The effect 
of geometry of the end cap on antenna react- 
ance has been shown in Figures 4, 12, and 18 
of Chapter 2.) This increases the shunt ca- 
pacity presented to the oscillator and decreases 
the internal resistance that can be had. There 
is obviously some optimum compromise between 
radiation resistance and shunt capacity for a 
fixed set of oscillator design factors. 

For a given cap and oscillator, the use of a 
matching network suggests itself. Practically, 
the network losses frequently cancel the ex- 
pected gain of sensitivity. The general proper- 
ties of this phenomenon are readily derivable. 
Let us assume an antenna of resistance A con- 
nected to a simple generator of voltage E by 



Figure 5. Block diagram for matching network 
for generator and antenna. 


way of a passive four-terminal network, as 
shown in Figure 5. 

The input resistance of the network is given 
by R = V/I G . We are interested in the value of 
dR/R for a given dA/A. We note first that 



and 


dR 

R 


die 

Ig ’ 


(7) 


The effect of increasing A by a small change dA 
is the same as would result from the introduc- 
tion of a voltage de — I A dA into the output cir- 
cuit. The incremental generator current dI G 
produced by de is, by the reciprocity theorem, 
the same as the increment dI A that would result 
from the introduction of de into the input cir- 
cuit. If we summarize certain properties of the 


SECRET 


86 


ELECTRONIC CONTROL SYSTEMS 


particular network in terms of a transfer con- 
stant T , so that 

I A = TV, dI A = TdV, (8) 

we readily find 

die = -TI A dA. (9) 

To evaluate equation (7) we need an expres- 
sion for I G in terms of I A . This is obtained in 
terms of the network efficiency. The power input 
is VI G , and the power output is I a 2 A. Hence, the 
power transfer efficiency of the network is 
given by 

I a 2 A I a A fifh 

e = m = T 77- (10) 

Combining equations (7), (9), and (10) gives 


dR _ dA 

I'‘T 


( 11 ) 


so that the power transfer efficiency 8 of the 
network is also the sensitivity transfer effi- 
ciency. 

This result suggests the existence of a gen- 
eral relation between sensitivity and radiated 
power, the source being unchangeable. We can 
generalize the oscillator circuit as comprising 
a triode, coupling network, and antenna. Viewed 
in this light, the idling bias V m is determined 
by supply voltage and tube design and does not 
depend upon circuit losses. We assume through- 
out that the grid drive conditions are such that 
the tube behaves as a constant-resistance gen- 
erator. This implies for the RGD that the plate 
current is approximately independent of load. 

The generalized circuit is shown in Figure 6, 
using the constant-current generator represen- 
tation for convenience. The network is char- 



Figure 6. Generalized circuit arrangement for 
coupling generator and antenna. 


acterized by the two parameters T and e, previ- 
ously defined. The net effect of the antenna and 
network is to present a resistance R to the gen- 
erator, as indicated in Figure 1. 


We have the following starting point rela- 
tions : 


Ia 

RIg 
elo 

V 

We immediately derive 0 

73 6 

AT 2 * 


= TV, 

= V, 

= TIaA, 


R 


R T - Ri 


( 8 ) 

( 10 ) 

( 3 ) 

( 12 ) 


Further, utilizing equation (11), we have 


o _ dV _ dV_ RRi 

b ~ dA/A ~ e dR/R ~ €Vc ° (R + Ri f 

Now the radiated power is 

= ISA = T 2 V 2 A = TWJA 
so that 


(13) 

, ( 14 ) 


S eR i Ri 

P~ A = T 2 V m AR = Tj 


(15) 


and is independent of T , s. 

This result is of great interest and is in 
agreement with intuition. For given triode op- 
erating conditions, the sensitivity is propor- 
tional to the power radiated. The components 
in the network can be adjusted for maximum 
voltage across the load resistance, and the sen- 
sitivity will be maximized. The unavoidable 
practical interdependence of T and 8 does not 
affect the relation between sensitivity and 
power. 

The above discussion reduced the ideal gen- 
erator to the triode itself, with V » essentially 
a tube parameter. In practice, the idling bias 
Foo is defined as the bias with the radiation 
load A removed but all other network compo- 
nents untouched. This practical definition is 
needed, since the presence of the network is re- 
quired for oscillation. From this experimental 
viewpoint, the effect of the network transfer 
constant is to adjust the internal resistance as 
seen by the antenna. The inefficiency of the net- 
work is expressible as a fixed loss load shunted 

c Equation (12), if differentiated, would imply 
( dR/R ) = (dA/A). This procedure is not legitimate, 
since both T and e are functions of A. 


SECRET 


RADIO-FREQUENCY SYSTEMS 


87 


across the antenna. This reduces the laboratory 
idling bias and also lowers the source resist- 
ance as seen by the antenna. It has been found 
that attempts to increase the step-up ratio of 
the network also increase the losses of the net- 
work, so that the optimum circuit arrangement 
for high-resistance antennas is a compromise 
between high bias and load matching. 118 ’ 121 

Experimental Determination of Sensitivity 

Throughout the early stages of the develop- 
ment, all measurements of sensitivity were 
measurements of the combined effects of oscil- 
lator and antenna performance. Reference is 
being made to the pole-test procedure discussed 
in Chapter 2. It suffices to repeat here only 
that this is a direct measurement of the signal 


laboratory evaluation. Laboratory tests are also 
much quicker and much more convenient, espe- 
cially when several parameter adjustments are 
being compared. 

Standard laboratory oscillator testing in- 
cludes taking a load curve and measuring the 
grid bias for various load values. The values 
used form a geometric sequence so that the data 
points are uniformly spaced on semilog paper 
(see Figure 7). Since standard commercial log 
paper is logarithmic to the base ten, the slope 
dV/d(\og R) must be multiplied by In 10 = 
2.303 to obtain the sensitivity S, which is 
dV/d { In R ) . The sensitivity can, however, be 
conveniently read from a tangent to the curve 
by noting the change of ordinate along the 
tangent corresponding to two abscissas whose 



Figure 7. Typical data points for experimentally determined loading curve ( E g ). Curve labeled S' 
shows sensitivity or slope of E g curve. 


voltage generated upon approach to ground. 
When suitable r-f load resistors became avail- 
able, and the radiation resistance had been 
measured, the oscillator sensitivity S as deter- 
mined in the laboratory was found to check 
closely with its value derived from the pole 
tests. (The derivation is the reverse of the 
process of predicting function height for a 
given oscillator sensitivity.) The experimental 
difficulties of pole-testing, in combination with 
ground screen diffraction effects, generally 
make this test method less accurate than the 


ratio is e = 2.718. Thus holding a straightedge 
tangent to the load curve at the point of interest 
and noting the intercepts of the straightedge 
with the vertical lines R = 1 and R = 2.7, or 
R = 3.7 and R — 10 allows computation of the 
sensitivity as the difference of the ordinate 
values of these intercepts. 

Proximity fuze oscillators, like any trans- 
mitters, are tested on dummy radiation loads. 
The reaction-type units RGD and POD are in- 
sensitive to small load reactance errors and can 
be tested on resistor loads. The ultra-high-fre- 


SECRET 


88 


ELECTRONIC CONTROL SYSTEMS 


quency resistors of the x /2- and 1-watt size, 
F - l /2 and F-l, manufactured by the Interna- 
tional Resistance Corporation, have been found 
satisfactory. Although the true values of these 
resistors at high frequency are not the same as 
the d-c values, the percentage difference does 
not vary seriously with resistance value. As 
discussed in Chapter 2, this allows the employ- 
ment of a self-consistent set of resistors where- 
in the unit is only approximately the ohm. 
Since radiation resistances are automatically 
measured in terms of this same unit, proper 
dummy loading and load curves are readily 
obtained. 

In the case of oscillator-diode type fuze, 
wherein the antenna circuit is sharply reso- 
nant, the dummy antenna must present not 
only the correct resistive component but also 
the correct reactive component of impedance. 
For various practical reasons, such as keeping 
r-f currents out of the power supply leads and 
metering leads, it has been found necessary to 
shield the fuze exciting cap properly from the 
laboratory environment. Enclosure of the fuze 
oscillator head in a metal shield box normally 
introduces more antenna shunt capacity than is 
introduced by mounting the fuze on a missile. 
To compensate for this, a low-loss inductor is 
made a part of the dummy antenna and 
shunted across the fuze to be tuned or meas- 
ured. This inductor is designed to parallel reso- 
nate the excess capacity introduced by the 
shield box. The power loss in the inductor is 
compensated by appropriate choice of dummy 
load resistor, so that the resistive component 
of the inductance combines with the test re- 
sistance to present the correct net load. 

For test operation of the complete metal 
parts assembly of a fuze, the shield box must be 
rigid and relatively small. (The shield box for 
tuning adjustments forms a 2-ft cube.) Since 
the fuze is vigorously vibrated in the final test 
chamber to search out microphonic defects, a 
directly connected dummy antenna is not 
usable. The simulated load is capacitatively 
coupled to the exciting cap, and the load imped- 
ance is connected between the pickup plate 
and the chamber. The inductive and resistive 
components of this impedance must be em- 
pirically adjusted for proper operation. The 


operating grid bias (or diode voltage) is meas- 
ured as a quality check, but no actual sensi- 
tivity measurement is made. The voltage check 
for production consistency is sufficient with a 
sampling test for oscillator sensitivity. 

The load curve slope determination of sensi- 
tivity is an indirect measurement. Several 
schemes for direct dynamic measurement of 
sensitivity have been proposed. These are all 
based on the use of a resistance which varies 
sinusoidally at an audio-frequency rate and can, 
therefore, be used either for measuring oscil- 
lator sensitivity or the overall Michigan sensi- 
tivity of the fuze. As all these direct dynamic 
methods of measuring sensitivity are necessar- 
ily signal simulators, they have already been 
discussed in Section 2. 12. 10 

One dynamic loading arrangement not in this 
category has had laboratory use. It is a device 
that allows the load curve to be exhibited on an 
oscilloscope, showing the existence of any oscil- 
lator instabilities and generally simplifying the 
process of investigating component changes. 
The desired load curve is voltage versus logar- 
ithm of resistance. If the load resistance is 
caused to vary exponentially with time, then 
time becomes proportional to the logarithm of 
the load resistance, and the normal linear time 
base of the oscilloscope is appropriate for dis- 
play of the voltage. The arrangement used com- 
prised the dynamic plate resistance of a triode 
for the oscillator load, with an appropriate uni- 
directional pulse of exponential decay applied 
to the grid of the auxiliary triode. Correct 
choice of the fixed bias on the grid relates the 
dynamic plate resistance to the added bias in 
the desired linear fashion. 

Practical Oscillator Design 

It has not been found possible to design com- 
pletely an RGD oscillator on paper. Certain 
adjustments must be empirically determined, 
and the associated phenomena are not thor- 
oughly understood. 

Experience has shown that adjustment of 
the oscillator parameters to make the oscillator 
behavior approach that of the ideal generator 
results in the greatest stability and reproduci- 
bility of operation. The feedback is adjusted 
by varying the plate circuit inductance to the 


SECRET 


RADIO-FREQUENCY SYSTEMS 


89 


end that the plate current is substantially inde- 
pendent of load. There is a considerable range 
of grid drive (feedback) that will satisfy this 
condition. 

Within this suitable range of operating con- 
ditions, we find that increasing the drive re- 
sults in higher grid bias and plate current with 
lower internal resistance. The increase of bias 
tends to increase the sensitivity; the decrease 
of internal resistance usually tends to lower the 
sensitivity. This effect arises in the high-shunt 
radiation resistances encountered, leading to an 
increase of mismatch with decreased internal 
resistance. 

These two conflicting factors lead to a rela- 
tion between sensitivity and drive which has a 
maximum. In practice the oscillators have usu- 
ally been designed empirically for this compro- 
mise of maximum sensitivity under normal ra- 
diation conditions. 

The value of the grid leak resistor is opti- 
mized quite simply. Variation of the grid leak, 
ceteris paribus, results in a parallel variation 
of grid bias and an opposite variation in plate 
current. Thus larger leak resistances give 
higher bias with less plate current, hence also 
higher internal resistance, until a plateau is 
reached. Still larger resistance values give 
negligible improvement, and eventually lead to 
squegging. Fortunately, when antisquegg sta- 
bilization is used the plateau can be reached 
and still allow a safety factor of 2 for stability. 

With the NR-3A triodes, 47,000 ohms was 
most commonly used for the grid leak. The T-51 
fuze used a 33,000-ohm leak, with slightly 
higher plate current. (See Figures 14 and 15.) 


31,3 Radiating System 

The mechanical details of the radiating sys- 
tem have been discussed in Chapter 2 along 
with the corresponding field patterns and radi- 
ation resistance values. In this chapter, the 
effect of the choice of radiator upon circuit de- 
sign will be discussed. 

The original “whip antenna” was basically 
a trailing wire, base loaded with inductance. 
This presented a relatively low-radiation re- 
sistance, and was accordingly series tuned. The 


oscillator was inductively coupled to the an- 
tenna circuit. A tuned diode circuit was loosely 
coupled to a second point in the antenna circuit, 
thus providing a means of measuring the an- 
tenna current and its variations. This bomb 
tail fuze served to prove the feasibility of prox- 
imity fuzes and was soon discarded in favor of 
an engineered assembly. 

The second stage in the development of the 
exciting arrangement was the substitution of 
a conical cap for the trailing whip. The imped- 
ance of this was sufficiently high to permit of 
parallel loading, the antenna feed points (cap 
and body) being connected across the diode 
tuning coil. Early models used a variable series 
coupling condenser between the cap and coil. 
This was done mainly to allow the vernier tun- 
ing adjustment to be made externally, the mov- 
able center screw of the simple cylindrical 
vernier condenser being threaded through a 
nut on the apex of the cap. Corona effects to be 
discussed later forced the abandonment of this 
scheme. The same arrangement was used in the 
first production of MC-382 rocket fuzes. In this 
case the corona problem was minor, but the 
mechanical instability of the condenser, and the 
complications of construction, left much to be 
desired. These several problems were solved 
by making the tuning adjustment from the 
base of the fuze, so that the cap could be direct- 
connected to the diode coil, and operate at d-c 
ground potential. 

Further variations of the end cap resulted in 
the antenna ring used on T-50 and related 
fuzes. (See Figures 4 and 5 of Chapter 1.) 
This design yielded medium radiation resist- 
ance values, which were readily matched to the 
oscillator, with relatively low fixed shunt ca- 
pacity. The ring also acted as a mechanical 
guard for the wind vane and as an electric 
shield against effects of bearing looseness and 
vane end-play. 

The latest variation of the end cap is found 
in the T-132 and T-171 mortar fuzes. (See Fig- 
ure 6 of Chapter 1.) In these designs the cap 
has grown in proportions until it is used as the 
housing for all components of the fuze except 
the oscillator and detonator mechanism. This 
makes it feasible to locate a turbo-generator 
power supply in the fuze nose. 




90 


ELECTRONIC CONTROL SYSTEMS 


An interesting antenna problem arose in the 
case of the 3-in. antiaircraft rocket. The insu- 
lated gap in this case was between the rocket 
motor and body, or about one-third of the total 
length from one end. The radiation resistance 
was of the order of 50 to 100 ohms. The loca- 
tion of the insulator required it to be mechani- 
cally rugged, and this automatically introduced 
high shunt capacity. The final design of insu- 
lating “coupler” had 40-ppf shunt capacity. 

It had been found with experimental low- 
capacity couplers that series feed of the an- 
tenna was convenient. The antenna load was 
simply inserted into the ground return of the 
diode coil. Proper load coupling occurred for a 
total antenna shunt capacitance of about 15 ppf. 
All attempted designs of coupler not exceeding 
this capacity failed to meet mechanical 
strength tests, so that attention was turned to 
the high-capacity rugged designs. 

The final 40-q|if design was incorporated into 
the circuit by shunt resonating 25 ppf of its 
capacity, leaving in effect a 15-ppf coupler. This 
tuning was noncritical and was accomplished 
by connecting approximately IV 2 in. of heavy 
wire across the coupler. 

Another exceedingly low-resistance antenna 
was encountered in experimental work on tail 
fuzes for the 4,000-lb and larger bombs (T-40 
and T-43). The tail structure of these bombs is 
sufficiently large to be used as a shunt-excited 
portion of the antenna, the feed points being 
the end of the fin structure and the bomb body. 

The remaining antenna structures are those 
designed for transverse excitation: the dipole 
and the loop. These both present exceedingly 
high parallel-radiation resistance, because their 
maximum dimensions are so small compared to 
the usable wavelengths. From the circuit stand- 
point, the loop is ideal. It is used as the plate- 
to-grid inductance of a Colpitts oscillator; the 
interelectrode capacitances complete the cir- 
cuit. It has been found advisable to add ca- 
pacity from triode grid to ground to balance 
the potential distribution of the loop and mini- 
mize longitudinal excitation. The loop is, how- 
ever, a very inefficient radiator in such small 
dimensions. Its series radiation resistance 
varies as the fourth power of its radius, meas- 
ured in terms of the wavelength. 


Early dipole-exciting circuits used the 
dipoles as end loading of the grid-plate Colpitts 
oscillator coil. Higher sensitivity was obtained 
by inductively coupling a dipole loading coil to 
the oscillator coil. The two coils were inter- 
wound on a double-threaded form for close 
coupling. Maximum sensitivity was obtained by 
winding the antenna coil with about one turn 
more than the oscillator coil. The radiation re- 
sistance presented to the antenna coil is about 
140,000 ohms. A convenient sensitivity check 
was made by noting the change of grid bias 
RGD or plate current POD when a 100,000-ohm 
load was presented to an otherwise unloaded 
fuze. Theoretically, two load voltage measure- 
ments bracketing the operating point are needed 
for a sensitivity approximation. (The approxi- 
mation involved is that of replacing the tangent 
slope by a secant slope.) Both these load re- 
sistances must be finite. In practice, all oscil- 
lators operating at loads higher than 100,000 
ohms can be checked satisfactorily by finding 
the voltage drop for the 100,000-ohm load. This 
is essentially an empirical measure of the re- 
sponse of the oscillator to light loads but can be 
justified as a good approximation to equation 
(4). 

S = Foop(l - p) = Foo(l - P ) = F ro - F, (16) 
for p = 1, i.e., light loading. 

314 Tube Characteristics 

General Requirements and Restrictions 

Problems arising in the development of tubes 
for Division 4 radio proximity fuzes did not 
stem from technical considerations alone. Deci- 
sions of military policy at staff level introduced 
extraneous technical problems of sizable diffi- 
culty, as will appear from the following brief 
historical review. 

In the first successful demonstration of the 
radio proximity fuze, February 1941, standard 
electronic tubes were used. These were obvi- 
ously too large for fuze application and pre- 
sented serious microphonic problems. Accord- 
ingly, cooperative programs were set up with 
Raytheon Production Corporation and the Syl- 
vania Electric Products Corporation (then Hy- 


RADIO-FREQUENCY SYSTEMS 


91 


grade-Syl vania) aiming at the design and pro- 
duction of small tubes with the desired electric 
and mechanical characteristics. First contacts 
were on the usual customer-to-manufacturer 
basis and did not involve development con- 
tracts. Practically any hearing-aid tube could 
withstand the low accelerations involved in the 
prospective bomb and rocket applications. The 
real problems were (1) reduction of micro- 
phony to an order of 30 db better than hereto- 
fore realized in the best hearing-aid tubes; 
(2) securing of extremely stable and relatively 
high-output oscillator performance from the 
small-sized tubes involved; and (3) the devel- 
opment of suitable diode and thyrafron tubes. 

The fuze circuit rendered microphony and 
self-noise in the triode oscillator of paramount 
importance, with diode and pentode micro- 
phonics of next importance and thyratron 
microphony of least importance. By the early 
summer of 1941, reasonably promising triode 
and pentode designs were under way and con- 
tractual arrangements had been made with the 
two companies and others for continued devel- 
opment on all four tube types. Such arrange- 
ments were handled through Division A, 
NDRC, of which Division 4 (then Section E) 
was a part. 

Concurrently with this program, Section T, 
Division A, NDRC, conducted a parallel devel- 
opment program with these and other tube 
manufacturers on a similar family of tubes for 
the shell-type radio proximity fuze. Here spe- 
cial emphasis was placed on tube ruggedness, 
with the requirement that a setback of 20,000# 
should be successfully withstood. Tube mi- 
crophony was apparently not as serious a prob- 
lem for Section T use, partly because of a some- 
what different lower power oscillator arrange- 
ment, but primarily because the centrifugal ac- 
tion of the spinning shell tended to keep the 
tube element supports in a fixed position. 

On August 26, 1941, Dr. Richard C. Tolman, 
Chairman of Division A, NDRC, appointed a 
committee to coordinate the two tube programs 
with A. J. Dempster as chairman, L. Grant 
Hector representing Section T, and Harry Dia- 
mond representing Division 4, then Section E. 
Contractors were informed of this setup. Both 
programs were prosecuted in parallel with Sec- 


tion T emphasis on ruggedness and Section E 
emphasis on microphony and oscillator per- 
formance. It is of interest to note that elements 
of design introduced to make a tube nonmicro- 
phonic go a long way toward making the tube 
rugged. The correlation is by no means 1-to-l 
but, curiously, the reverse is not nearly so true, 
i.e., making a tube rugged does not insure free- 
dom from microphony. 

As will appear from the following more tech- 
nical discussions, many of the expedients for 
making tubes nonmicrophonic, such as special 
filament tension springs, four-pillar base con- 
struction, etc., were known to the art but were 
also essential in the Section T program for 
making tubes rugged. High-level policy re- 
quired that Section E tubes be designed so that 
in the event of prior compromise they would 
not reveal details of rugged tube design to the 
enemy. This policy was based on firm military 
considerations and was followed in good faith. 
However, it placed the Section E tube program 
in the anomalous position of having no recourse 
to certain technical expedients known to be 
available to the enemy. 

Hence, up to the time the mortar fuze design 
was begun, problems of Section E tube design 
consisted of how to attain the desired electric 
and mechanical performance without making 
the tubes too rugged. Since maximum rocket 
setback was of the order of 400# and some 
safety factor was essential, it was specified that 
tubes should withstand 2,500# as a lower limit, 
but under no circumstances should such tubes 
withstand more than 10,000#. The curious situ- 
ation ensued wherein anything that made a 
tube ‘‘not too rugged’’ was greeted with delight 
and tested with the hope that it would not affect 
tube microphony. One exception, a GE micro- 
thyratron, simulating lighthouse tube construc- 
tion, was permitted by common consent, since 
it was not used in the Section T fuzes and no 
expedient could be found whereby it would not 
withstand 20,000 to 30,000#. 

In addition to the general requirement that 
the tubes fail at high accelerations, the follow- 
ing types of structure (most of which were well 
known to the art) could not be used: (1) four- 
pillar construction for supporting grid and 
plate elements, (2) a coil spring cantilever 



92 


ELECTRONIC CONTROL SYSTEMS 


(mousetrap construction) for supporting the 
filament under proper tension, (3) cross- 
press construction for the lead end of the tube, 
and (4) grid sleeves and grid stops. (See refer- 
ence 33 of Chapter 1.) 


effect on the feedback. The circuit can be con- 
sidered as a Hartley with additional capaci- 
tance across the plate and grid coils or, equally, 


Triodes 


The design starting points were the sub- 
miniature hearing-aid amplifier pentodes al- 
ready in existence. Omission of the screen and 
suppressor grids and replacement of the fila- 
ment by a more powerful one made a triode 
suitable for experimentation. The power re- 
quirements on the triode were so relatively 
heavy that Raytheon put in two filament 
strands to obtain the desired emission and life. 

The final design of the Raytheon tube was 
designated NR-3A and has approximately the 
following characteristics. 


Filament voltage 
Filament current 
Amplification factor 
Mutual conductance 
Cutoff bias 


1.4 v nominal 
220 ma 

1,600 micromhos | at - 7 ' 5 v bias 
—23 v 




The above data were obtained at the nominal 
plate voltage of 140. 

A photograph of the NR-3A triode is shown 
in Figure 8 and of the subassembly of the same 
tube in Figure 9. 

The Sylvania triode NS-3, which was used in 
MC-382 battery fuzes but not in generator- 
powered fuzes, has approximately the following 
characteristics at nominal plate voltage of 140. 

Filament voltage 1.4 v nominal 

Filament current 140 ma 

Amplification factor 9.3 / , . 

Mutual conductance 1,350 micromhos ) at ' v ias 

Cutoff bias — 15 v 

This tube was not used in bomb fuzes be- 
cause of its low microphonic stability. This 
point will be discussed later. 

These triodes work well in any of the stand- 
ard oscillator circuits. The oscillator-diode type 
fuzes used the quasi-Hartley circuit shown in 
Figure 10. If the grid-filament and plate-fila- 
ment interelectrode capacities were negligible, 
this would be a Hartley oscillator using the 
grid-plate capacitance as the “tank ,, condenser. 
In practice the first two capacitances are of the 
same order of magnitude as the last, so that the 
interelectrode capacitances have considerable 


Figure 8. NR-3A triode (left) and NR-2 diode 
(right). Arrows show crimps to support mica 
spacers. Scale shown is 1 in. 


as a Colpitts with an added coil tap. If the in- 
ductive feedback ratio is not equal to the capa- 
citative feedback ratio, local circulating cur- 



rents are created in the grid and plate branches 
of the circuit, introducing extra power losses 
and sometimes critical response to coil adjust- 




RADIO-FREQUENCY SYSTEMS 


93 


ments. This circuit operated satisfactorily in 
the 120- to 140-mc range, but was unsatisfac- 
tory at 150 me. 

Later circuits, RGD and POD, used pure Col- 
pitts connections (cf. Figures 11 and 12). 
These perform quite uniformly over the whole 
range of 50 to 200 me that has been used. For 
stable efficient operation, the NR-3A triode re- 
quires driving to approximately 2-ma average 
grid current. That is, in the oscillator-diode 
arrangement, where a low-impedance power 
source was required, the maximum usable grid 
leak was 15,000 ohms and the minimum bias 
for proper operation was 30 v, corresponding 
to 2-ma direct grid current. In practice, this 



Figure 10. Typical quasi-Hartley oscillator used 
in oscillator-diode fuze circuits. 

current fell between 2 and 3 ma. In the RGD 
oscillator, grid leaks of 33,000 and 47,000 ohms 
have been used with the idling bias in the range 
60 to 100 v, so that the grid current under no 
load conditions was 1.5 to 2 ma. Since the opti- 
mum grid drive is affected by many factors, 
such as power output, internal resistance of the 
oscillator as a generator, stability of oscilla- 
tion, and sometimes maximum grid bias, it is 
not determinable from any simple theory of the 
oscillator. It is, therefore, a purely empirical 
observation that, in general, the NR-3A should 
operate at about 2-ma grid current (this is for 
a nominal plate supply of 140 v) . 

The plate current of this triode may be any- 


thing in the range 7 to 14 ma, depending on 
the oscillator frequency and application. The 
subject triode has not been found useful at 



Figure 11. Typical Colpitts oscillator used in 
RGD fuze circuits. 


lower plate current because of power (and sen- 
sitivity) requirements. Higher plate current 
does not normally occur with optimum oscilla- 
tor design, but the average current for actual 
fuze designs has been found to be approxi- 
mately proportional to oscillator frequency in 
a given type of application and circuit. 

All electric circuits are in some degree sub- 



Figure 12. Typical push-pull Colpitts oscillator 
used in POD fuze circuits. 

ject to spurious signals. The sources of these 
signals range from statistical thermal fluctua- 


SECRET 


■ 


94 


ELECTRONIC CONTROL SYSTEMS 


tions of resistance to intermittent connections. 
In the battery-powered fuzes, the most impor- 
tant noise sources were inside the triode. This 
electric noise can be classified as self-noise and 
microphonics. Self-noise arises without appre- 
ciable mechanical stimulus of vibration or 
shock. Microphonics refers to those noises 
which are mechanically induced. 

The early triodes frequently were noisy 
(self-noise) due to the presence of charred lint. 
The lint had become charred in the baking op- 
erations and formed a conducting carbon fila- 
ment which eventually would bridge two tube 
elements. The electrostatic forces on the lint 
were responsible for its short-circuit seeking 
habits. Occasionally one end of a lint piece 
would firmly adhere to the plate and the other 
to the grid, forming a miniature carbon fila- 
ment incandescent lamp. In such cases, the lint 
would often be more luminous than the cathode. 
The lint problem was eliminated by improved 
manufacturing techniques. Another source of 
noise was electric leakage between leads on the 
outside of the glass press. This was traced to an 
alloying of the glass and a metallic oxide 
formed on the external leads in the pressing 
operation. There was one lead which was cut 
off next to the glass, since it was merely an 
anchor. By postponing the cutting off until 
after the seal was made, this wire did not get so 
hot and did not burn. The extra length served 
to conduct heat away. No more trouble was had 
from this source after the new procedure was 
established. Interelectrode leakage paths in- 
side the envelope, i.e., on the mica spacers, can 
also produce noise. This phenomenon is dis- 
cussed under the diode noise problem, as it was 
not serious in triodes. 

The most difficult problem in designing the 
triode was the reduction of microphonic effects. 
In an oscillator, any variations of either the 
low-frequency parameters of the triode of the 
interelectrode capacitances produce variations 
of the high-frequency output and the developed 
grid bias. The microphony problem became 
acute with the transition from battery power 
to generator power, because the rotating sys- 
tem associated with the generator necessarily 
produces vibration. In fact, as the missile 
changes speed, so does the rotating system, and 


the frequency of the mechanical vibrations is 
apt to sweep across some resonant frequency of 
the tube structure. 

The most serious resonance was that of the 
electrode assembly as a cantilever spring. Fur- 
thermore, if the elements are not tightly cou- 
pled at the free end, the plate can vibrate 
relative to the grid and filament. If the mica 
spacer is sufficiently snug to prevent this, then 
the whole assembly is a stiffer cantilever but 
can still vibrate with respect to the surround- 
ings. Of course, the bending of the structure 
will also introduce a small relative motion be- 
tween grid and anode. Microphony of this type 
was practically eliminated by pressing the glass 
envelope in against the mica spacers on both 
sides. This is referred to as crimping. Since the 
electrode support posts lie along the major di- 
ameter of the cross section of the triode, crimp- 
ing of the flat sides of the bulb (preventing 
motion along the minor diameter) greatly in- 
creases the rigidity of the structure. This con- 
struction was adopted as standard in the 
NR-3A triode and was also introduced into the 
diodes as a general precaution, although the 
need for it in the latter case was not demon- 
strable. The arrows in Figure 8 point to the 
crimps on the triode. 

The filamentary cathode itself cannot be 
made rigid. Its resonance frequencies are kept 
well above the audio range by proper tension, 
but freak low-frequency disturbances can be 
generated. These apparently arise from the 
nonlinear phenomena associated with finite vi- 
bration amplitudes of the filament. If the fre- 
quency of the driving force applied to the fila- 
ment is slowly varied, the resulting vibration 
amplitude increases according to a normal 
resonance curve as the filament resonant fre- 
quency is approached. As the amplitude in- 
creases, the resonance frequency is changed by 
virtue of the finite amplitude. When the driving 
frequency passes the moving resonance, the re- 
sulting decrease of amplitude moves the reso- 
nance back, further decreasing the amplitude. 
The net result is a sudden drop of amplitude at 
driven frequency to the value predicted by the 
simple resonance curve. The sudden change of 
average tension excites a transient at the na- 
tural frequency which produces a beat with the 


SECRET 


RADIO-FREQUENCY SYSTEMS 


95 


driven frequency. Thus, 100-c beat transients 
have been observed in a filament driven at ap- 
proximately 5,000 c. The extreme sharpness of 
resonance of the filament allows this phenome- 
non to occur for slight variations in driving 
frequency. The details of the effect have not yet 
been investigated mathematically. 

Another possible source of microphonics is 
associated with low filament tension. The fila- 
ment passes through a small hole in the top 
mica and then runs to a tension spring. For 
various reasons, it is best to pull the filament 
against the edge of this hole by placing the 
spring off center. With low tension it is con- 
ceivable that under vibration or shock the 
filament will slip on this edge, producing 
noise. 

Generally, high filament tension is indicated, 
but variations in tension adjustment can lead 
to filament breakage. The simple construction 
utilizing a cantilever spring is sensitive to pro- 
duction variations of spring displacement. This 
situation can be improved by the use of a longer 
cantilever. The extra length is incorporated by 
coiling the cantilever into a horizontal helix, 
with the last turn straightened out tangentially. 
This spring is made of ribbon. Another spring 
design that has been used can be readily de- 
scribed as two such springs of wire, one left- 
handed and one right-handed, joined by a canti- 
lever hairpin for the filament support. This 
type of construction is referred to as the mouse- 
trap spring and was not used in the NR-3 
triodes because it was believed it would make 
the tubes too rugged. 

The electrode structure must be rugged to 
withstand rough handling of the fuze as well as 
the high accelerations encountered in mortar 
and shell firing. Ruggedness is a simple matter 
of structure design, the problems arising in 
making a sufficiently rugged assembly as 
simply and cheaply as possible, and of such 
design as to be readily adaptable to the mass 
production techniques of tube construction. 
The filamentary cathode is the only element 
which cannot be braced and solidly supported, 
but its mass is very low. Its ruggedness is in- 
creased by shortening it, since its total mass is 
thus reduced, but its tensile strength is un- 
affected. 


Diodes 

The major requirements on the diode de- 
tector were small size, low filament power, and 
reasonably low plate resistance. The low fila- 
ment power was requisite to battery-powered 
fuzes. With the advent of generator power, it 
was found advantageous to increase the diode 
filament ruggedness at the expense of addi- 
tional heating power ’ by increasing the fila- 
ment diameter. The average characteristics of 
the final design, Raytheon NR-2A, are 

Filament voltage 0.60 v 

Filament current 70 ma 

Effective plate resistance 50,000 ohms 

This apparently high plate resistance is satis- 
factory, since the diode (see Figure 8) ordi- 
narily works into a 1-megohm load resistance. 

At high frequency, and high applied voltage, 
the capacitative anode-cathode current is an 
appreciable fraction of the normal filament 
current and can cause burnout. A more serious 
burnout problem was caused by stray induc- 
tive coupling between the oscillator and the 
diode filament circuit. 

There have been occasional indications of 
diode microphony, but these have been nebu- 
lous. Crimping was adopted, as in the triode, 
for a general precaution. The high inverse 
voltage on the diode did lead to self-noise prob- 
lems, involving leakage paths on the mica elec- 
trode spacer. These leakage paths could be 
eliminated in most cases by “sparking” the 
tube. This consisted of playing a high-fre- 
quency discharge over the surface of the tube, 
which apparently burned the conducting ma- 
terial off the mica. A still more effective remedy 
consisted of spraying the mica surface with a 
thin coating of Alundum. The resulting rough 
surface inhibits the formation of leakage paths. 

The major source of leakage was found to be 
stray deposits of “getter” material. Redesign 
of the getter holder was the final step in elimi- 
nating leakage. 

315 Spurious Signals and Circuit Stability 
Component Noise 

Not all noise and microphony arises in the 
tubes. Occasionally unstable resistors and con- 
densers are found which generate noise in op- 


SECRET 


96 


ELECTRONIC CONTROL SYSTEMS 


eration, but this phenomenon is not sufficiently 
frequent to be of concern. Most of the residual 
microphony can be traced to poor workman- 
ship (or design), involving such factors as in- 
securely anchored connecting leads and coil 
windings and imperfect metallic contacts in the 
mechanical assembly. Insufficient restraint of 
the triode envelope often results in severe mi- 
crophony because of th£ resulting variation of 
capacity, when the triode moves relative to its 
surroundings. The major part of all micro- 
phony is induced by vibration of the power- 
supply generator and associated rotating sys- 
tem. Dynamic balance of a one-piece rotating 
system has eliminated much of this difficulty. 
(See Section 4.6.) 

The power supply itself can introduce noise 
by supplying a modulated plate voltage to the 
oscillator. Noise modulation of the supply volt- 
age can arise from irregular axial motion of 
the generator magnet (rotor) as well as from 
such obvious defects of operation as rubbing 
of the rotor on the pole faces and intermittent 
rotor-stator contact via stray metallic particles. 
Instantaneous fluctuations of rotating speed, 
such as can occur through the slack of a shaft 
coupler, result in fluctuations of output voltage 
if the generator is operating on a nonconstant 
portion of its voltage-speed curve. Some noise 
has been traced to variation of contact between 
rectifier elements, but this is eliminated by a 
combination of careful element manufacture 
and high stack pressure. 

Corona Effects 

Early model oscillator-diode fuzes employed 
the customary series d-c load resistance on the 
diode rectifier. This automatically put the recti- 
fied signal on the antenna cap and isolated the 
cap from ground by the load resistor, normally 
1 megohm. Field experience indicated that 
change of bomb potential in flight produced 
small corona effects. The high-resistance cap 
isolation caused the production of a signal- 
voltage input to the amplifier, when the charge 
on the bomb plus fuze was redistributed. Field 
effects of random function and peculiar carrier 
modulation could be reproduced in the labora- 
tory under the influence of a 300-kv d-c gen- 
erator. 


This source of malfunction was completely 
eliminated by maintaining the antenna cap at 
the same d-c potential as the bomb. This was 
accomplished by grounding the cap, as far as 
direct current or audio is concerned, through 
the antenna coil and using a shunt load on the 
diode output. All fuzes since have incorporated 
the d-c grounding of the antenna. The effect of 
this circuit change was reported as follows: 218 

The rearrangement of the diode coupling circuit in 
the ROB [abbreviation for radio-operated bomb fuze] 
showed satisfactory solution of the problem of elimi- 
nating operation of the fuze by static voltage dis- 
charges. With the previous arrangement, the fuze 
would function when placed in the neighborhood of a 
- 30-kv field; with the new scheme, the fuze withstood 
visible corona and other discharges when in the neigh- 
borhood of a 300-kv field. 

Unstable Oscillation 

When attempts are made to increase the 
power output sensitivity of an oscillator, un- 
stable oscillation conditions are frequently en- 
countered. For example, increasing the grid 
leak resistance increases the bias, internal re- 
sistance, and sensitivity of the oscillator while 
decreasing the plate current. If the critical 
value of resistance is exceeded, however, the 
oscillator becomes unstable. This instability 
may be great enough to cause alternate periods 
of oscillation or may be mild enough to cause 
only a low-percentage modulation of the oscil- 
lation amplitude. The first effect is the familiar 
intermittent oscillation, often attributed to a 
large time constant in the bias circuit. The 
whole gamut of instabilities is incorporated 
into the term “squegging.” 

Operation under intermittent oscillation con- 
ditions offers interesting possible advantages 
resulting from the high ratio of peak power to 
average power. This was investigated to some 
extent in connection with battery power to re- 
duce the average anode current. A peak voltage 
detector, such as the diode in the oscillator- 
diode fuze, can “remember’’ the antenna volt- 
age from pulse to pulse, and the sensitivity 
with an intermittent oscillator is approximately 
the same as that with a steady oscillator whose 
amplitude is equal to the peak amplitude of the 
former. This type of operation is not possible 
in the RGD, since the rectified output is also 


SECRET 


RADIO-FREQUENCY SYSTEMS 


97 


the oscillator bias. In fact, loading curves show 
that the RGD average bias is very insensitive 
when the oscillation is intermittent. Detection 
of target approach with the RGD might be 
feasible by detecting the change of intermit- 
tency period with radiation load. Experiments 
by A. Stratton in England (communicated ver- 
bally) show that the pulse repetition rate is a 
smooth sensitive function of radiation resist- 
ance. Investigation of this scheme requires 
the development of a variable time-delay reflec- 
tion line for a dummy antenna, since for non- 
steady signals the effect of target reflection can- 
not be replaced by an impedance. The lack of 
reflected signal during the first few cycles of 
each pulse (while the oscillation is building up) 
can well make a fundamental difference be- 
tween field performance and loading curves 
representing a steady-state condition. 

Just as steady oscillation would be fatal to a 
fuze designed to operate intermittently, squeg- 
ging in any form is likely to be fatal to any 
fuze of the present types. It is not the inter- 
mittency itself that produces early functions, 
since the normal repetition rate is of the order 
of 100 kc and so does not affect the amplifier. 
Rather, it is the marginal stability of the oscil- 
lator that does the damage. For example, varia- 
tion of the supply voltages can convert a steady 
oscillation into an intermittent one ; the change- 
over produces transient pulses which are 
passed by the amplifier. Under some threshold 
conditions, a sensitive superregenerative oper- 
ation can occur, amplifying thermal voltages 
and other hiss noises. 

In the early unprotected RGD units, margin- 
ally high values of grid resistor occasionally 
produced the modulation phenomenon of the 
second type described above. No mention of 
this particular phenomenon has been found in 
the literature. Only a qualitative theory has 
been evolved. 

Intermittent oscillation arises from an un- 
stable condition in which the oscillator grid 
bias increases until plate current and oscilla- 
tions cease. This extreme bias decays exponen- 
tially with time at a rate determined by the 
product of the grid-leak resistance and the bias 
storage capacitance. When the bias decays to 
a value at which oscillation will start, the oscil- 


lation starts and grows in amplitude until the 
bias is again too large for the tube to operate. 
This starting and stopping of oscillation re- 
peats periodically. 

The instability represented by the appear- 
ance of self-modulation is fundamentally of the 
same nature but of a lesser degree. In this case 
the oscillation amplitude and grid bias increase 
with time, but, before the tube is rendered in- 
operative, a temporary equilibrium between 
amplitude and bias is reached. Because of time 
lag between a change of amplitude and the 
resulting change of bias, this equilibrium is not 
stable but represents a condition where the 
oscillation amplitude is not sufficient to main- 
tain the bias. Both start to decrease and con- 
tinue to decrease until a lower temporary 
equilibrium is reached. At this low equilib- 
rium the oscillation amplitude is more than 
sufficient to maintain the bias, so that the bias 
and amplitude again increase. The phenomenon 
is periodic. 

Both types of instability arise because of the 
presence of an operating point (combination 
of grid bias and oscillation amplitude) that 
represents an unstable equilibrium. An un- 
stable equilibrium is an equilibrium condition 
in which any small deviation of the operating 
point produces conditions that force the operat- 
ing point still further from equilibrium. If no 
restoring force is encountered by the operating 
point, intermittent oscillations result. If suffi- 
cient restoring force is encountered on both 
sides of the unstable equilibrium point, the 
operating point will oscillate over a range. If 
the inherent instability is increased, that is, by 
increasing the grid leak resistance, the range 
of operating point variation will increase and 
finally intermittent oscillation will result. 

The stability of the original operating point 
depends on the relation between oscillation am- 
plitude and grid bias and on the time lag with 
which the bias variation follows a correspond- 
ing amplitude variation. An operating point is 
statically stable if a small arbitrary change 
of oscillation amplitude produces a greater 
change of bias than would be needed to keep the 
bias in equilibrium with the amplitude. A stat- 
ically stable operating point will be dynamically 
unstable if the bias change does not occur rap- 


SECRET 


98 


ELECTRONIC CONTROL SYSTEMS 


idly enough. This dynamic instability can be 
produced by the use of too large a time con- 
stant in the grid-bias circuit. 

The dynamic stability of the RGD oscilla- 
tors has been increased by a circuit whose 
essential elements are shown in Figure 11. The 
resistor R p in conjunction with the condenser C 
comprises a means of reducing dynamic insta- 
bility by obtaining a voltage increment from 
the rate of change of amplitude and introduc- 
ing this voltage increment onto the grid in such 
a manner as to make the bias anticipate any 
change of amplitude and prevent its occur- 
rence. 

The voltage drop across the stabilizing re- 
sistor R p is proportional to the anode current. 
For small variations of oscillation amplitude, 
the anode current variation is proportional to 
the amplitude variation. Hence, the voltage 
drop across the resistor has a time rate of 
change proportional to the rate of change of 
oscillation amplitude. The terminal of this re- 
sistor nearer the anode is connected by a small 
capacitor to that terminal of the grid leak re- 
sistor R g which is nearer the grid. This capaci- 
tative coupling between the stabilizing resistor 
and the grid leak causes an incremental volt- 
age, which is approximately proportional to the 
rate of change of amplitude, to appear across 
the grid leak. 

Static stability of an oscillator is normally 
achieved by the self-biasing action of a grid 
leak. If the amplitude of oscillation actually in- 
creases, the bias is increased, producing sta- 
bility. This stabilizing circuit achieves dynamic 
stability by increasing the bias, if the oscillation 
amplitude starts to increase. Thus the bias is 
corrected if the amplitude has only a rate of 
change, without waiting for the change to actu- 
ally occur. This means that if the amplitude 
starts to change, the grid bias anticipates the 
change from the fact that it started and pre- 
vents the actual change from occurring. This 
anticipation of a change is the antithesis of the 
ordinary time lag with which the bias follows 
an amplitude change. 127a 

Antimicrophony Circuits 

The audio-frequency signal in a proximity 
fuze is produced by detection of a slightly 


modulated high-frequency oscillation. The 
problems of microphony are intimately associ- 
ated with this low degree of modulation, which 
is normally about % 0 of 1 per cent. This im- 
plies that accidental variations of the steady 
diode voltage, oscillator bias, or plate current 
(according to the fuze type) need be only a 
fraction of a per cent in magnitude to generate 
spurious signals as large as normal firing sig- 
nals. Highly selective amplifiers are used to 
discriminate against these microphonic volt- 
ages (see Section 3.2). Various schemes have 
been proposed to alleviate the situation, and 
these are all designed to neutralize essentially 
the steady voltage and thereby increase the 
fractional modulation produced by a target re- 
flection. 

In the oscillator-diode fuze, futile attempts 
were made to neutralize the steady high fre- 
quency applied to the diode. One such sugges- 
tion was to arrange the antenna and detector in 
a bridge circuit, so that the antenna load varia- 
tion would appear as a bridge unbalance. No 
workable arrangement has been devised. An- 
other scheme applicable only to the oscillator- 
diode fuze was based on the fact that oscillator 
microphonics produce almost identical signals 
on the oscillator grid bias and diode output. 
These can be balanced against each other in 
a push-pull transformer coupling arrangement. 
This worked in the laboratory but would not 
in practice because of the exacting require- 
ments on tuning accuracy and equality of d-c 
grid bias and diode output. 

In the RGD, where the signal appears on the 
oscillator bias, a simple means is available for 
reducing the response to plate-supply voltage 
variations. The grid leak may be returned to 
the plate supply, instead of to ground, if its 
resistance value is appropriately increased so 
that the same grid current will result in the 
same grid bias. This can be done for only one 
operating condition, since the bias is no longer 
proportional to the grid current. There will be 
a point on this resistor which will be at ground 
potential, since the grid end is negative and the 
plate end positive. Since the RGD oscillators 
are sufficiently linear to develop a bias propor- 
tional to the plate-supply voltages over a wide 
range, the cold point on the resistor will re- 



RADIO-FREQUENCY SYSTEMS 


99 


main cold if the plate supply varies. On the 
other hand, variations of antenna load, which 
vary the bias but obviously do not affect the 
power supply appreciably, will generate a volt- 
age at the initially cold point. It is apparent 
that this tapped resistor is a voltage divider 
on the signal and reduces it in the ratio 
E B /(E g + E b ), where E g is the magnitude of 
the bias, and E B the plate-supply voltage. Es- 
sentially, the same results can be had for pass- 
band and higher frequencies by returning the 
grid to the plate supply for audio frequencies 
only. This eliminates possible difficulties aris- 
ing from the application of positive bias while 
the cathode is warming up. This modification is 
made by using the normal ground return on the 
grid leak and coupling the plate supply to the 
amplifier input on the other side of the blocking 
condenser which isolates the oscillator bias 
from the pentode. These arrangements are sat- 
isfactory for rejection of power supply noise, 
when the oscillator works into a given load, 
such as any one missile. Installation of the fuze 
on a different missile generally upsets the bal- 
ance, as the operating bias is different. 

Another scheme has been proposed for the 
RGD, but not experimentally investigated. Its 
operation is based on the fact that a normal 
RGD oscillator draws a plate current which is 
independent of load, so that a high audio im- 
pedance in the plate circuit would not affect 
normal operation. If any audio voltage appear- 
ing across the impedance were properly cou- 
pled back to the grid, a high degree of degener- 
ation (negative feedback) could be introduced 
for spurious signals without producing loss of 
sensitivity. This is possible because most spuri- 
ous signals (microphones or supply fluctua- 
tions) generate in-phase variation of grid bias 
and plate current. 

Arming Pulse 

Safety of the fuze is achieved by mechanical 
interruption of the powder train as well as in- 
terruption of the electric circuit of the detona- 
tor. Details are discussed in Section 3.3. Neces- 
sarily, the process of arming a fuze involves 
completion of the detonator circuit, and this 
can conceivably give rise to an arming pulse 
which may prematurely fire the fuze. 


Stray r-f currents are usually present to 
some extent in the power supply leads and, 
therefore, couple into the detonator circuit. The 
presence of any r-f current in the detonator, 
however small, indicates coupling between this 
circuit and the oscillator. Closure of this circuit 
will, therefore, change the load on the oscilla- 
tor. Since the oscillator is very sensitive to load 
changes, a firing strength transient can occur 
even though the r-f current in the detonator is 
apparently negligible. A by-pass condenser 
across the detonator will not usually eliminate 
this pulse, but a small series choke will. 

A related type of pulse occurs in mortar 
fuzes of the T-171 and T-132 types. In these 
designs, power supply and amplifier are en- 
cased in the exciting cap, so that the detonator 
firing current must traverse the antenna split. 
This requires a choke in one detonator lead; 
the ground return is through the antenna coil. 
In this arrangement, the choke does not suffi- 
ciently isolate the detonator, since the total gap 
potential is across the choke. Connecting the 
detonator is essentially the same as connecting 
the choke across the antenna, and it produces a 
strong pulse. Thorough by-pass of the detona- 
tor-switch combination would eliminate the 
pulse, but complete by-passing at this point is 
not always feasible from the production design 
standpoint. Circuits have been devised to im- 
munize the fuze against this pulse and are de- 
scribed in later sections. 

Additional Precautions 

There are several problems of circuit detail 
that have not been discussed above, being too 
minor to warrant special headings. A few of 
these will be mentioned here as being worthy 
of special precaution. 

The grid-bias variations are fed into the 
audio amplifier. The input circuits of some 
amplifiers can present enough shunt capacity at 
high frequency to cause squegging in the oscil- 
lator. A series isolation resistor of 100,000 
ohms is sufficient protection. This resistor, in 
conjunction with grid-to-ground by-passing at 
the pentode, also helps to reduce stray r-f volt- 
ages on the pentode grid. Stray radio frequency 
at this point will be rectified, changing the bias 
on the pentode and hence changing the gain. 


SECRET 


100 


ELECTRONIC CONTROL SYSTEMS 


Stray r-f currents also reach the pentode via 
the filament leads. It has been found advisable 
to connect a fairly large capacitance, 150 to 
250 across the filament supply close to the 
triode. These stray currents in the power leads 
also produce electric coupling between the 
oscillator and moving generator parts. Vari- 
able contact between shaft and bearings can 
then produce spurious signals. To minimize this 
effect, the plate-supply lead is also heavily by- 



A 


Figure 13. Oscillator-diode circuit for T-50 fuze, 
diagram arranged to correspond to photograph. 

passed to ground as it leaves the oscillator 
compartment. 


3,1,6 Typical Designs 

Details of the various fuzes are presented 
later in the “catalog” chapter (Chapter 5). The 
purpose of this section will be fulfilled by pre- 
senting prototype oscillators. 

The oscillator-diode type is exemplified by 
the T-50; the circuit is shown in Figure 13R 
and the component placement in Figure 13A. 


The oscillator-diode circuit had several dis- 
advantages. An obvious economic and space 
disadvantage is in the need for a diode and 
associated components. Accurate tuning of the 
diode-antenna circuit is a nuisance in produc- 
tion, and temperature and aging effects fre- 
quently detune the fuzes. The outstanding de- 
fect of this circuit is its microphony associated 
with frequency variation of the oscillator. Un- 
less the diode circuit is tuned exactly, its sharp 


TEST point 



B 

A is photograph of oscillator block. B is circuit 


response makes it a frequency discriminator, 
resulting in spurious signals for any micro- 
phonic variation of triode capacitances. The 
RGD, on the other hand, is relatively broad in 
its tuning effects. That is, a given change in an- 
tenna capacity or oscillator frequency results 
in a change of grid bias which is very small 
compared to the corresponding change in diode 
voltage in the OD type of fuze. Detailed com- 
parisons are presented in the bibliography. 51 

Fuzes of the RGD type require no individual 
oscillator adjustments and are surprisingly 
uniform in production. The design used in 


SECRET 


RADIO-FREQUENCY SYSTEMS 


101 


the T-50 series of fuzes is illustrated in Fig- 
ure 14. 

The dipole antenna-type fuze is illustrated by 


coupling. Circuit and layout are shown in Fig- 
ure 15. 

The simplest circuit of all is that used in the 



Figure 14. RGD circuit for T-50 fuzes. A is photograph of oscillator block. B is circuit diagram 
arranged to correspond to photograph. 


T-51. The dipole is inductively coupled to a T-172 mortar fuze with a single-turn loop an- 
Colpitts oscillator, the antenna coil being in- tenna. This consists of a simple squegg-stabil- 
terwound with the oscillator coil for close ized Colpitts oscillator, using the loop for the 



Figure 15. RGD circuit for T-51 fuze. A is photograph of oscillator block. B is circuit diagram arranged 
to correspond to photograph. 


SECRET 


102 


ELECTRONIC CONTROL SYSTEMS 


circuit inductance. The circuit is shown in Fig- 
ure 16. 


31,7 Generalization of Sensitivity Concept 

The sensitivity of the r-f unit has been de- 
fined as S = R(dV/dR ) . This is sufficient for 
practical purposes, where the antenna circuit 
is operated at resonance. If, however, the an- 
tenna circuit is nonresonant or if reactance is 



Figure 16 . Oscillator circuit for use with loop 
antenna (T-172). 

effectively introduced in the form of an off- 
frequency external signal, it is necessary to 
know the more complete behavior of the r-f 
unit. 

The two-terminal equivalent of an antenna 
approaching a target is a fixed impedance or 
admittance plus a rotating additional imped- 


d This section may be considered as appendix ma- 
terial to Section 3.1.2. 


ance or admittance, provided the antenna does 
not approach the target too closely. That is, 
the incremental impedance or admittance pro- 
duced by reflection of the antenna field changes 
slowly in magnitude but undergoes a continu- 
ous phase rotation (cf. Figure 1 of Chapter 2). 
Under the normal operating condition wherein 
the fixed portion of the antenna impedance is 
real (resistive), the maximum and minimum 
values of instantaneous detector voltage corre- 
spond to phase angles of 0 and 180 degrees for 
the incremental impedance. The complete com- 
plex detector sensitivity to impedance changes 
then reduces to a pure resistance sensitivity for 
computing the magnitude of the audio-voltage 
output. 

The complete sensitivity could be expressed 
in terms of either impedance or admittance. 
The admittance evaluation is more convenient, 
since combinations of resistance and reactance 
can readily be placed across the fuze antenna 
terminals in parallel with any antenna imped- 
ance that may be present, whereas it is not 
feasible experimentally to insert impedance ele- 
ments in series with the antenna. Dealing with 
admittances thus leads to an automatic ignor- 
ing of the inherent shunt capacity from the 
fuze cap to fuze ground. 

If we write the antenna admittance as 
A — C — jB, then the detector voltage will be 
a function of both C and B. The term C is, of 
course, the reciprocal of the parallel resistance 
R in the formula S — R (dV/dR ) . Therefore 


V = V(C,B), 
dV = dC dC + dB dB ' 


(17) 


The physical condition that the incremental ad- 
mittance is a rotating vector requires 


so that 


dC = | dC | cos 6, 
dB = \dC\ sin 0, 


dV 


C w\ = cgeose + cgsine, (18) 


indicating that dV is a sinusoidal voltage incre- 
ment. We require its magnitude. 

dV 


C 


dC 






(19) 



AMPLIFIER SYSTEMS 


103 


We so define these terms as to make the equa- 
tion read 


S = 



y/ Sc 2 + Sb 2 > 


( 20 ) 


so that the complete sensitivity is given by the 
quadrature addition of the conductance sensi- 
tivity S c and the susceptance sensitivity S B . 

We immediately note that 



1 dV 
R d(l/R) 


- R dV - 
“ ~ R dR ~ 


( 21 ) 


so that our former simplified definition is pre- 
served when the susceptance (or reactance) 
sensitivity vanishes. 

Both quantities S c and S B are readily meas- 
ured in the laboratory as slopes of detector volt- 
age versus values of antenna shunts. 

There is one direct application of this formula 
of interest to this section. It gives the solution 
to the question of the effect of antenna circuit 
detuning on sensitivity, a question of practical 
significance in oscillator-diode fuzes. 

Consider the fuze as a constant-current gen- 
erator feeding the tuned diode-antenna circuit, 
with internal admittance A i — C t — jB,. Then 
the r-f voltage developed will be 


E = 


( 22 ) 


l(C t + C) - j(Bi + B)Y 
and the diode will yield a detector voltage pro- 
portional to the magnitude of E lt 


V = kI[(Ci + Cy + (Bi + B) 2 ]~K (23) 

When the fuze is properly tuned (maximum 
detector voltage) we have 


V = kI(C + Ci)~\ 


r dV -kIC 
dC (C + C;) 2 



where V 0 is the value of V when C — 0, i.e., the 
idling voltage. This is our original sensitivity 
formula, except for the trivial change of sign. 
If the fuze is detuned, 


V = kl [(C + Ci) 2 + (B + Bi) 2 ]~\ 

C % = - kIC(C + Ci) [(C + cy + {B + 


_ -C(C + CQV» _ „ 

C kiy ~ Sd ’ (25) 

where S D represents the sensitivity when the 


fuze is detuned. We already have for the tuned 
sensitivity 



(26) 


in terms of the tuned voltage. Thus the ratio 


Sd = C + Cj JP = JP 

S T kl V T 2 V t v 1 ; 

shows that the sensitivity falls off with detun- 
ing as the cube of the voltage. 

But if the voltage has been decreased by mak- 
ing B -f B t 0, then the response to variations 
in B must be taken into account. We must com- 
pute the complete sensitivity 


Now 


s = \4s c 2 + s B 2 . 


Sb = c % = ~ kIC ( B + s *)- 


(28) 


[(c + cy + (b + Bym 

C{B + Bi) V 3 


(kiy 


(29) 


and 


s =Vs B 2 + s c 2 = VSb 2 + sy 


— jjepy \/(b + By + (c + cy 

to be compared with 


PC 
kl ’ 

(30) 


yielding 


« _ Vr 2 C 
6 T kl ’ 

S V 2 
S T ~ V t 2 ’ 


(31) 

(32) 


so that actually detuning drops the sensitivity 
only as the square of the voltage and not as the 
cube. This is important in setting specification 
limits on the accuracy of tuning in production. 


3-2 AMPLIFIER SYSTEMS e 

321 General Requirements 

The amplifier receives the signals from the 
r-f section of the fuze and is required so to 
modify them that the desired signal will operate 

e This section was prepared by Bertrand J. Miller, 
Ordnance Development Division of the National Bureau 
of Standards. 


SECRET 



104 


ELECTRONIC CONTROL SYSTEMS 


the thyratron at the appropriate time and place. 
Since the amplifier input signal consists of sev- 
eral components (desired signal due to reflec- 
tion from target, noise due to tube and circuit 
vibrations, hum due to a-c filament operation 
and imperfect filtering of B supply voltage, 
etc.), these modifications consist of the follow- 
ing changes. 

Amplification of the Desired Signal. In most 
applications, the signal generated by the r-f 
section is small compared to variations in strik- 
ing voltage (critical bias) of the thyratrons, 
due to tolerances in manufacture, variations in 
supply voltages, temperature and other operat- 
ing conditions. The amount of amplification re- 
quired is different for fuzes for different appli- 
cations and different for different trajectories 
encountered with the same application. Thus 
fuzes for different purposes require different 
amplifiers. The variation with trajectory usually 
imposes a requirement on the shaping of a cer- 
tain sector of the gain-frequency curve of the 
amplifier, since the different trajectories are 
generally characterized by different signal fre- 
quencies at the desired point of operation. The 
maximum voltage gain required in the fuzes 
developed by Division 4 has usually been of the 
order of 150 times; the frequency region con- 
taining the desired signals has been between 
50 and 350 c. 

Attenuation of TJndesired Signals. The most 
prominent signals, aside from those due to 
presence of the target, are microphonic noise 
and hum due to a-c operation. The latter, of 
course, consists of an approximately sinusoidal 
signal, of fundamental frequency varying from 
700 c up to, in some cases, several thousand 
cycles. The amplitude is generally of the order 
of the filament supply voltage, that is, 1 to 
IV 2 v. After sufficient refinement in oscillator 
tube design, the microphonic noise was also 
restricted to high frequencies, generally above 
2,000 c. Even after all refinements of tube con- 
struction and selection processes developed to 
date, considerable noise in the high-frequency 
region can be expected. Under the severe vi- 
bration conditions encountered sharp spikes 
of the same order as the hum voltages can still 
be expected from the most carefully chosen 
tubes. 


The preceding considerations impose two ad- 
ditional design conditions on the amplifier. In 
order to reject these undesired signals, which 
are of the order of volts, and function on the 
desired signal of the order of hundredths of a 
volt, the amplifier is required to have a sharp 
high-frequency cutoff. In addition, the ampli- 
fier is required to be linear up to large input 
voltages at high frequencies to avoid genera- 
tion of voltages in the pass band by rectification 
of noise and hum envelope variations or by 
generating difference-frequency terms from two 
nearly equal noise or hum voltages or their 
harmonics. (The presence of two mechanically 
independent filaments in the triode oscillator 
made this last circumstance seem especially 
likely. Laboratory vibration tests showed that 
shock excitation of the filament resonances is 
very common, and that the two resonant fre- 
quencies generally differ very slightly, by an 
amount frequently in the signal-frequency re- 
gion.) Of course, any serious overload at the 
always present, hum voltage frequency and 
magnitude would keep the amplifier perma- 
nently paralyzed and prevent amplification of 
signal frequencies. 

Finally then, all these requirements are to be 
met in an amplifier which is compact, not criti- 
cal either to supply voltages or to variations in 
component values due to manufacturing toler- 
ances, insensitive to very wide ambient tem- 
perature and humidity conditions, both during 
the short time of use, and for long periods of 
storage, rugged enough not to generate noises 
of its own, under conditions of severe vibration, 
and in some cases capable of withstanding ac- 
celerations up to 12,000#. 

3 ' 2 ' 2 Selection of Amplifier Characteristics 

Three general types of amplifier characteris- 
tics are required: one for the longitudinally 
excited fuze for use against airborne targets, 
one for the longitudinally excited fuze for use 
against ground, and one for the transversely 
excited fuze for use against ground. The ruling 
factors and the resultant characteristics are 
quite different, so the three types will be dis- 
cussed separately. 



AMPLIFIER SYSTEMS 


105 


Antiaircraft Target 

The central problem in the case of an air- 
borne target is the design of a fuze, usable on 
a variety of rockets of different physical dimen- 
sions, to produce a burst when the rocket passes 
approximately abeam of its target (see Section 
1.3). Relative velocities between target and 
missile of 700 to 1,900 fps can be expected. 
Function near the ideal burst surface is desired 
out to passage distances of 70 ft or more. 

The signal input to the amplifier under these 
conditions has been discussed in Sections 2.11.2 
and 2.11.3. 

The important characteristics are decrease of 
signal frequency from a maximum of 2 Vfk 
(frequently called the head-on doppler fre- 
quency) to zero and an increase of signal ampli- 
tude ; most of both changes take place in a lim- 
ited region near the target. Thus a peaked 
amplifier with maximum gain somewhat below 
the head-on doppler frequency would tend to 
localize bursts in the appropriate region. Too 
sharp an amplifier cannot be used, since calcu- 
lations show that, in the region where burst is 
desired, the signal frequency is changing rap- 
idly (as high as 50 per cent change in frequency 
per cycle). The breadth of the amplifier re- 
quired to realize much gain on such a signal 
would presumably make the precise location of 
the peak frequency less critical. The best loca- 
tion for the peak and the gain required were 
determined empirically. 

The empirical studies consisted of field tests 
and of laboratory tests with the “drum genera- 
tor” on the audio-signal simulator discussed in 
Section 2.12. As a result of such tests, the fol- 
lowing factors were established : 

1. For an r-f sensitivity of approximately 15 
v and a fuze directivity pattern approximately 
like that of a half-wave dipole and a carrier 
frequency in the vicinity of Brown reference, 
the required amplifier sensitivity should be such 
that about 30-rms-mv input signal (at fre- 
quency of peak gain) will fire the thyratron. 

2. The peak frequency can be located almost 
anywhere below two-thirds of the head-on dop- 
pler frequency with reasonably good burst 
placement. For function nearly abeam of the 
target rather than earlier on the trajectory 
(see footnote b of Chapter 1) the amplifier peak 


frequency equal to about one-half the head-on 
doppler would be optimum. One-half is a nom- 
inal value, since the head-on doppler frequency 
obviously varies with rocket velocity, target 
velocity, launching plane velocity, and relative 
orientations of these. The normal figure refers 
to the case of medium rocket velocity, equal at- 
tacking plane, and target plane velocities, and 
an overtaking aspect for the rocket. Any other 
orientation of target and rocket velocities would 
give a higher head-on doppler frequency, and a 
smaller value of the ratio of peak frequency 
to head-on doppler. A smaller value of this ratio 
would give bursts closer to the ideal surface in 
the overtaking aspect, but would probably be 
too low for the nose attack and other high 
relative-velocity aspects. Not much experimen- 
tal information is available on this point, since 
most testing was done with a stationary target, 
and it was not possible to mock-up the head-on 
aspect by adding twice a combat-plane velocity 
to the normal rocket speed. 1 

A cutoff on the high-frequency side at a rate 
which reduces the gain by a factor of 10 at one 
and one-half to two times peak frequency and 
continues on down at a slightly smaller slope 
was found to be fast enough, reducing the gain 
to approximately unity at power-supply fre- 
quencies. Adjustment of the low-frequency side 
of the gain curve is ordinarily made to give a 
half-gain width of approximately half the peak 
frequency. Drum generator studies (see Sec- 
tion 2.12) show that at this width the gain of 
the amplifier to the type of signal actually en- 
countered in use is nearly the same as the 
steady-state gain for a sine wave of the same 
instantaneous frequency for frequencies in the 
vicinity of peak, and that objectionable delays 
are not encountered. 

The manner in which the circuit problems 
incident on realization of an amplifier having 
the above characteristics were solved will be 
discussed in Section 3.2.3. Time may be taken 
here to point out, however, that a different 
solution is possible, as pointed out in an early 
NDRC report. 1 This solution involves using 
only the decreasing frequency characteristic of 
the signal. The signal wave form is amplified 
and clipped into a square wave; the duration 
of each cycle is then measured. Firing of the 


SECRET 


106 


ELECTRONIC CONTROL SYSTEMS 


thyratron is accomplished when a long enough 
half-cycle occurs. This attack was not pursued 
at that time inasmuch as it required the use 
of two tubes, whereas an amplifier could be 
designed to give reasonably good burst place- 
ment with a single pentode. Where space is 
available, however, the alternative solution may 
have other advantages which warrant further 
investigation of this approach. 

Some study has also been made of amplifier 
requirements for fuzes suitable for air-to-air 
bombing. Here one deals with low relative 
velocities, and, in addition, a different orienta- 
tion of relative velocities in the most important 
tactical case. For the rocket case, with emphasis 
on the overtaking aspect, the rocket velocity is 
along the rocket axis in a coordinate system 
fixed in the target. This is a fortunate situation 
in one respect, since this state of affairs can be 
simulated in field tests with a stationary target. 
This state of affairs does not exist in the case 
of bombing a formation from above. The result 
of the difference is a slower rate of increase of 
signal from the r-f section, and, in general, a 
displacement of the point of maximum signal 
away from the point on the trajectory of closest 
approach. Details of the computations are re- 
ferred to in the bibliography; 113 no experi- 
ments were carried out by Division 4. 

Ground Approach, Longitudinal Excitation 

The problem here is the development of a 
fuze which will give substantially uniform burst 
heights on a variety of bombs, dropped from 
different altitudes and at different airplane 
speeds; the same fuze to be useful both for 
level-flight release and dive bombing if possible. 
In order to show the degree to which it is pos- 
sible to harmonize these requirements by ap- 
propriate amplifier design, the requirements 
for one fuze of this type will be presented in 
detail. 

We choose for the purpose of this illustration, 
the requirements for a fuze operating at 75 me, 
with use on the M-30 (100-lb GP) and the M-81 
(265-lb fragmentation) bombs being contem- 
plated. This fuze is also usable on the M-66 
(2,000-lb GP), and with somewhat less effec- 
tiveness, on the M-64 (500-lb GP) ; but here we 
will consider only the first two bombs. 


Because of the varying degree of mismatch 
between oscillator impedance and radiation 
load, the fuze r-f section will not have the same 
r-f sensitivity on the two bombs; we take as 
representative values a sensitivity of 11 v on 
the M-30 and 14 v on the M-81. Further, al- 
though the variation is slight, the directivity 
patterns are somewhat different, due to the dif- 
ferences in effective electrical length; the por- 
tions of the pattern of tactical interest are 
shown in Figures 17 and 18. 



Figure 17. Directivity pattern for M-30 bomb 
at Brown frequency, longitudinal excitation. 
Curve shows detail for small angles off nose of 
missile. 

In addition, the ballistic coefficients of the 
two bombs differ, so that similar release condi- 
tions result in slightly different terminal con- 
ditions (velocity and angle of approach to the 
ground) . 

Function heights of the order of 2 to 7 wave- 
lengths will be considered; for some of these, 
near the nulls of the directivity pattern, it is 
necessary to consider the contribution of the 
induction field (inverse R 2 field, see Section 
2.10). For this reason, function heights for 
nearly vertical approaches do not vary directly 
with amplifier gain. 

Computation will be made of the amplifier 
gain necessary to give a function height of 50 ft 
over a surface with reflection coefficient equal 
to 0.7 for various combinations of release alti- 
tude and plane speed, both for level flight and 
dive bombing. The computations are made on 



AMPLIFIER SYSTEMS 


107 


the basis of the theory developed in Sections 2.9 
and 2.10. 101> 140 

Curves of voltage gain versus frequency re- 
quired for these various conditions, based on 



Figure 18. Directivity pattern for M-81 bomb, 
Brown frequency, longitudinal excitation. Curve 
shows detail for small angles off nose of missile. 

an assumed holding bias of 5.3 v on the thyra- 
tron, are shown in Figure 19. The frequency 
ranges shown on each curve correspond to re- 
lease altitudes from 2,000 to 20,000 ft for the 
level-flight cases, and 1,000 to 10,000 ft in the 
dive-bombing cases, which is assumed to con- 
tain all the range of interest. Outside these 
ranges, the gain should be low. 

Examination of Figure 19 shows that the 
requirements for different release conditions 
are conflicting, so that a compromise is neces- 
sary. In making such a compromise, the follow- 
ing considerations are general : 

1. The high-frequency end of each curve cor- 
responds to a steeper angle of approach than 
the low-frequency end. At steeper angles the 
induction (inverse R 2 ) field is more important. 
Consequently, the height of function varies 
more nearly with the square root of gain at 
high frequencies than at low. This gives greater 
freedom of design in this region of the spec- 
trum. 

2. If an oscillator-diode type of fuze is con- 
templated, the tuning problem must be consid- 
ered. In the case of the fuze under discussion, 
all production models were oscillator-diode. 
These were tuned on the M-30, so that the full 
11-v sensitivity assumed was probably very 


closely realized on that bomb. Because of a 
slight difference in reactance of the two ve- 
hicles at the feedpoint, however, the fuze was 
somewhat detuned on the M-81, resulting in a 
reduction of the average sensitivity by about 
5 per cent. 

3. Very high gains should be avoided as far 
as possible without loss of effectiveness, since 
high gain obviously increases the probability of 
malfunction. 

One compromise actually used is also shown 
on Figure 19, the curve being an average curve 
for production units (Philco T-91, type 20 am- 
plifier). This fuze was designed in response to 
a request to give special weight to low-altitude 



Figure 19. Amplifier gain curves required for 
longitudinally excited fuzes for different bombs 
in different release conditions. 

The labeled curves represent conditions as follows: A, M-30 
bomb released at 200 mph in level flight; B, M-30 bomb 
released at 300 mph at level flight; C, M-81 bomb released 
at 200 mph in level flight; D, M-81 bomb released at 300 
mph in level flight; E, M-81 bomb released at 400 mph in 
60-degree dive; F, M-81 bomb released at 300 mph in 30- 
degree dive. Full curve represents a compromise gain- 
frequency characteristic for typical unit. 


and diving releases. The corresponding func- 
tion heights are shown in Figure 20, for the 
level flight cases and in Figure 21, for the dive- 
bombing cases. 




108 


ELECTRONIC CONTROL SYSTEMS 


Since the input signal in this application does 
not change in frequency or amplitude rapidly 
in the region where function is desired, steady- 
state calculations are adequate. However, for 
the purpose of determining amplifier delays, 
more precise calculations were made, making 
use of Borel’s theorem. According to the theo- 
rem, the response of any linear network can be 
computed for any form of input if one has 
either the network response to a unit step H (t) 
or a sharp spike of unit impulse H'(t ). 54 Fig- 
ure 22 shows H(t) and H'(t) for a typical am- 
plifier, and Figure 28 the delays computed. The 
computed delays are less than 5 ft for all tac- 
tical situations for the amplifier, and are not 
longer for the other amplifiers employed. 

For the fuzes at other frequencies, the re- 
quirements are very similar and will not be 
detailed here. The similarity extends even to 
maximum gain required, so that the changes 
consist primarily in frequency shifts, signal 



O 4000 8000 12000 16000 20000 


RELEASE ALTITUDE (FEET) 

Figure 20. Function heights computed from 
gain curve of Figure 19 for level flight release. 
The various curves represent conditions as 
follows: A, M-30 bomb released at 200 mph; B, 
M-30 bomb released at 300 mph; C, M-81 bomb 
released at 200 mph; and D, M-81 bomb released 
at 300 mph. 


discussion. Here, lower function heights are 
desired, of the order of 10 to 15 ft. The projec- 
tiles are much smaller than bombs and short 
compared to the carrier wavelengths proposed. 



Figure 21. Function heights computed from 
gain curve of Figure 19 for dive releases. For 
M-81 bombs, curve E is for a 60-degree dive at 
400 mph, and curve F is for a 30-degree dive at 
300 mph. 


As a consequence the radiation resistance is 
high and varies rapidly with frequency. The 
directivity pattern, however, is nearly inde- 
pendent of frequency for carrier frequencies 
below 135 me. Thus for low-carrier frequency, 
one expects low r-f sensitivity, but this is bal- 
anced by a larger scale factor (wavelength, A), 
and more important induction field contribution. 
(The latter is of great importance because of the 
low function height desired.) As a consequence 
of the interaction of these factors, it develops 
that an amplifier gain curve can be drawn 
which is optimum not just for one carrier fre- 
quency but for any carrier between 70 and 
130 me. It was also found possible to realize this 
gain-frequency curve (Figure 24) econom- 
ically. 130 


frequencies being proportional to carrier fre- 
quency for bombs with similar ballistics. 

The fuze for the mortar projectile using lon- 
gitudinal excitation merits a brief separate 


Ground Approach, Transverse Excitation 

The difference between the amplifier required 
in the case of a transversely excited fuze and 
that of the longitudinally excited fuze arises 


SECRET 


AMPLIFIER SYSTEMS 


109 


from the difference in the directivity patterns. 
In the longitudinal case, one has axial sym- 
metry about the axis of the bomb. The direc- 
tivity pattern is a minimum for vertical ap- 



Figure 22. Response of typical amplifier to a 
unit step function, H (t ) , and a short pulse of 
unit impulse, H' (£). 


proach, and increases rapidly as the angle of 
approach increases (angle between trajectory 
and vertical) for any orientation of the bomb 
about its axis. 

In the case of the transversely excited fuze, 
the directivity pattern is maximum for vertical 
approach. For angles of approach other than 
zero, the value of the directivity pattern de- 
pends somewhat on the orientation. For most 
tactical situations, however, the signal strength 
is nearly independent of release altitude and 
hence of signal frequency. A relatively flat gain 
curve is therefore required. For the carrier fre- 
quency used (about 150 me), and the bombs 
employed, the useful tactical range of altitudes 
gives a frequency range from 165 to 330 c. 

The value of the maximum gain is determined 
by the r-f sensitivity at the operating load and 


by the directivity pattern. Because of the high 
radiation resistance, and consequent poor match 
to oscillator impedance, sensitivities are lower 
than those encountered on most bombs with the 
longitudinal fuzes. The antenna gains were ap- 
proximately the same. However, the tactical 
range of approach angles centered near the 
maximum of the directivity pattern in the 
transverse types, instead of near the minimum, 
as was the case with the longitudinal types. 
The net effect of all these factors is a require- 
ment for somewhat less gain (for the same 
height) for the transverse fuzes. Production 
fuzes, however, were in fact built with approx- 
imately the same maximum gain as the longi- 



Figure 23. Amplifier input and output signals 
for various heights above ground, assuming ap- 
proach of 30 degrees with the vertical and 
vertical velocity of 790 fps. Assumed amplifier 
peaked frequency is 120 c. Carrier frequency: 
Brown. Solid curve represents input signal multi- 
plied by steady state gain; dashed line repre- 
sents output signal (inverted). 

tudinal fuzes and consequently gave somewhat 
greater heights of function. 

This amplifier is required to have a sharper 
high-frequency cutoff than the amplifier for 


SECRET 



110 


ELECTRONIC CONTROL SYSTEMS 


the longitudinal fuzes by virtue of the higher 
carrier frequency employed. This necessitated 
maintaining a high gain at 330 c, whereas the 



Figure 24. Gain-frequency characteristic curve 
required for trench mortar shell fuze, assuming 
carrier frequency compensation. 


highest frequency encountered with longitu- 
dinal types was 225 c. Since power-supply fre- 
quencies at arming may be as low as 700 c, a 
very rapid cutoff is required. 

3 2 3 Methods of Securing Required Gain 
and Shaping; Typical Circuits 

Axial Antenna Fuzes 

All amplifiers used in modern fuzes for non- 
rotating missiles are lineal descendants of the 
amplifier developed for the MC-382, the elec- 
tronic control part of the T-5 or T-6 fuzes. Here 
the shaping was accomplished by a feedback 
network similar to that employed in RC oscil- 
lators, using only resistors and condensers. With 
a network employing three series condenser- 
shunt resistor sections between grid and plate 
of single tube amplifiers, the following relations 
are noted : 

1. At low frequencies, the feedback ampli- 
tude is very small and phase shift is nearly 
270 degrees. 

2. At higher frequencies, feedback amplitude 
is larger and phase shift through network is in 
the vicinity of 180 degrees; this constitutes 
regenerative feedback. 


3. At still higher frequencies, feedback am- 
plitude is still larger and phase shift approaches 
zero, i.e., the amplifier becomes highly degen- 
erate. 

This principle is attractive because it gives 
promise of providing a sharp high-frequency 
cutoff, together with large voltage-handling ca- 
pacity in the high-frequency region, with the 
consequent freedom from cross modulation of 
large noise voltages. Consequently, the circuit 
was developed and used in the form shown in 
Figure 25, employing pentodes developed from 
hearing-aid tubes. 

One peculiarity of this circuit is perhaps 
sufficiently basic to warrant discussion here. 
The resistances R g , R 7 , and the parallel com- 
bination of R g and the source impedance, con- 
stitute a voltage divider which controls the 
amount of feedback. Since R G is of the order of 
megohms, and the impedance of the r-f section 
as an audio generator is of the order of tens 
of kilo ohms, it is evident that the amplifier 
characteristics depend markedly on the imped- 
ance of the source. Thus all amplifiers of this 
family required properly designed test circuits 
(see Chapter 7) which simulated the impedance 



Figure 25. Schematic circuit of feedback ampli- 
fier employed in T-5, T-6 fuzes. 


of the sources for which the amplifiers were 
designed. Similarly, some restrictions were im- 
posed on source design, since the amplifier pre- 
sented to the source an impedance varied radi- 
cally with frequency, even becoming negative 
in certain cases. 

The values used in this circuit will not be 
cited as typical examples, despite the historic 
interest of the circuit, for two reasons. First, 
the circuit was the last designed for battery 



AMPLIFIER SYSTEMS 


111 


operation ; the high-frequency cutoff was inade- 
quate for generator use with raw alternating 
current as a filament supply. Second, because 
of the status of tube de\*elopment at the time, 
many of the values represented compromises. 
Tube development and circuit development were 
proceeding simultaneously. At the time epoch 
corresponding to Figure 25, two reasonably 
satisfactory but different pentodes had been 
developed by different laboratories. The di- 
vergence in characteristics, however, was not 
so large that using both in the same amplifier 
was not feasible, by some judicious compromis- 
ing on values. 

A more typical amplifier, therefore, is shown 
in Figure 26. This is a type furnishing a gain- 
frequency curve of shape suitable either for 
airborne targets or for ground approach, with 
longitudinal excitation. It will be noted that 
the feedback voltage is now divided by a ca- 
pacity, rather than a resistance divider; at 
frequencies above peak frequency, this provides 
capacity loading on the input grid and improves 
the high-frequency cutoff. Further high-fre- 
quency attenuation is provided by the series 


tion. This scheme was adopted because it proved 
to be possible in this way to control peak gain 
with only minor effects on the frequency at 
which peak gain was realized. 

A typical gain-frequency curve is reproduced 
as Figure 27 ; also shown is the curve noted 
when the pentode grid side of both feedback 



FREQUENCY (CPS) 


Figure 27. Gain-frequency characteristic and 
flat gain characteristic given by circuit of Figure 
26. 



Figure 26. Later feedback amplifier circuit 
employed in generator-powered fuzes. Feedback 
circuit shown employs a feedback divider (Cu, 
Ci6> and gain control (Cs) . 

R-shunt C network in the thyratron grid cir- 
cuit. A higher gain level was sought and was 
obtained in part by increasing the feedback. 
This additional gain necessitated the provision 
of a feedback adjustment. A variable capacity C 
was provided for this purpose. The feedback 
network is designed to give too much feedback, 
so that gains are too high; adjustment of C 
introduces a controllable amount of degenera- 


loops is disconnected. It will be noted that the 
gain at peak frequency is multiplied by a 
factor of about 2.5 by the feedback; this is 
about the maximum amount of feedback usable 
if too sharp gain curves and undue dependence 
on variations in supply voltage are to be 
avoided. The gain without feedback is of course 
depressed by the various high-frequency atten- 
uating networks, and by the loading of the 
plate circuit by the feedback loop; the same 
tube in a conventional RC-coupled amplifier 
gives a gain of about 100 times with the supply 
voltages indicated. 

Within reasonable limits, the amplifier can 
be redesigned to give the same shaping at other 
peak frequencies by simply scaling the capaci- 
ties; this practice was largely followed here, 
with minor readjustment of values to commer- 
cially available ones where necessary. 

A somewhat different shaping was required 
for mortar fuzes, because of the rather differ- 
ent ballistic properties and conditions of use 
for these projectiles ; the requisite gain curve is 
shown in Figure 24. 


SECRET 


112 


ELECTRONIC CONTROL SYSTEMS 


Trans verse- Antenna Fuzes 

The relatively high flat plateau, with steep 
cutoff on the high side, required of amplifiers 
for transverse-antenna fuzes suggests the use 
of two peaks. This attack on the problem has 


TO RF 



Figure 28. Two-stage feedback amplifier for 
use with transverse antenna fuze. 


been pursued in various ways. Perhaps the most 
obvious is the use of two stages similar to Fig- 
ure 25 in cascade, with the feedback loops ad- 
justed to different peak frequencies. Another 
possibility is the use of two feedback loops in 



Figure 29. Gain-frequency characteristic for 
two-stage feedback amplifier of Figure 28. 


the same stage. Here a network similar to that 
of Figure 25 was employed for the higher 
frequency peak, and a network with series re- 
sistance and shunt capacity was used for the 
lower frequency peak. (This order was essen- 
tial since the degenerative feedback below peak 


frequency for the series C network was atten- 
uated, as was that above peak-frequency for 
the shunt C network.) Finally, the conventional 
feedback network to. provide the high peak, 
combined with an LC network for the lower- 
frequency peak, could be used. 

All these approaches were investigated. Lim- 
ited experience with the dual-feedback loop 
indicated a relatively high supply-voltage sen- 
sitivity; since other successful and economical 
solutions of the problem were available, this 
attack was not vigorously pressed. A typical 
two-stage solution is shown in Figure 28. Be- 
cause of requiring two tubes, this solution 
found little use ; however, it obviously has 



Figure 30. Schematic diagram for feedback 
amplifier with tuned choke input (used in T-51). 

greater flexibility and, as shown in Figure 29, 
can provide extremely sharp cutoffs which 
might be necessary in some applications. 

The solution of the problem which found the 
greatest practical use employed a series reso- 
nant LC network in the pentode grid for the 
low-frequency peak. The high-frequency peak 
was obtained by feedback ; the two circuits com- 
bined to give a very fast high-frequency cut- 
off, necessary in this case by virtue of the prox- 
imity between signal and generator frequencies. 
(This same fact was responsible for the fila- 
ment center tapping employed.) The feedback 
circuit thus still supplies the high-frequency 
grid degeneration which enables the amplifier 
to handle large high-frequency signals. The 
design of the feedback loop, as noted in Fig- 
ure 30 is conventional; the same type of gain 
control is used. 


, SECRET 



AMPLIFIER SYSTEMS 


113 


The low-frequency peak is supplied by the 
grid choke and C 3 ; the Q of this resonant cir- 
cuit is controlled by a series resistor. It is of 
interest to note that a low-impedance C bias 
source must be provided for in order not to 
broaden the resonance curve. 



Figure 31. Gain-frequency characteristic for 
choke input feedback amplifier. 


The type of M-8 head employing plate cur- 
rent rather than grid voltage variations was 
used in one bomb fuze with transverse excita- 
tion (T-82) and thus required a similar am- 
plifier-gain curve. Figures 32 and 33 show a 
typical circuit and gain curve. Here, trans- 



Figure 32. Schematic diagram for feedback 
amplifier with transformer input. (The switch 
shown below C15 is a sensitivity control.) 


former input to the amplifier is employed, the 
low-frequency peak being supplied by resonat- 
ing the transformer secondary ; the usual high- 
frequency feedback network being employed. 

Combination Amplifiers 
The applicability of a fuze to various missiles 


could be increased if it were possible to vary 
the amplifier shaping in the field by a simple 
adjustment. Thus, although the same general 
shaping is required in a rocket fuze for ground 
approach and for airborne targets, the required 



Figure 33. Gain-frequency characteristics of 
amplifier shown in Figure 32. High and low 
curves correspond to switch open and closed. 


peak frequency and gain are different. The 
same remark is true if it is desired to use the 
same type of fuze against airborne targets on 
rockets and on bombs. By the introduction of 
shorting switches, to cut additional feedback 
sections in or out, good approximations to two 
different ideal gain curves can be provided in 



Figure 34. Combination amplifier for use in 
air-to-air and air-to-ground applications. Switch 
S allows transfer from one application to the 
other. 

the same amplifier. Typical circuit and gain 
curves are shown in Figures 34 and 35. Since 


SECRET 



114 


ELECTRONIC CONTROL SYSTEMS 


operation of the switch consists in removing 
or inserting a screw from the chassis, the oper- 
ation is readily performed in the field immedi- 
ately before fuzing the projectile when the ap- 
plication is determined. 

A similar adjustment was investigated on 
some transverse-type fuzes to provide sensi- 



Figure 35. Gain-frequency characteristics for 
amplifier shown in Figure 34. Upper curve repre- 
sents air-to-air case, the other, air-to-ground. 


tivity control. Removal of a screw inserts a 
voltage divider in the amplifier, whose effect is 
to halve the gain and thus halve the expected 
height of burst. 


324 Properties of Pentodes 

The electric properties of the pentodes used 
in the amplifiers differed in some respects ac- 
cording to the manufacturer of the pentode. 
Average values are shown in the accompanying 
table. 



Raytheon 

Sylvania 

ge 2 

R p 

2.0 

1.6 

1.4 

Qm 

218 

195 

176 

U 

445 

310 

250 

Rscreen grid 

0.32 

0.27 

0.54 

If 

62 

60 

64 

Input 

impedance 

30 

10 

30 


megohms 

yumhos 

megohms 

ma 

megohms 
(measured 
at 60 c) 


The values cited above were not measured at 


the same element voltages for the different 
tubes, but at the operating voltages occurring 
at those elements when the tube was operated 
in a typical feedback amplifier, with 1.4-v A 
supply, 140-v B supply, and — 1.8-v C bias. 

Security requirements were imposed on the 
mechanical properties in part. (See Section 
3.1.5.) For the greater part of the time interval, 
including the development and tactical use of 
fuzes for nonrotating missiles, it was required 
that all tubes used must fail on a 20,000# cen- 
trifuge test. It proved possible to build tubes 
which would pass 2,500# with reasonable as- 
surance of failure at 20,000# ; accordingly, this 
level of ruggedness was chosen for the great 
majority of the tubes built for this program. 



Figure 36. View of three pentodes used in 
amplifiers for proximity fuzes. These are from 
left to right: GE pentode, Raytheon pentode 
NR-5, and Sylvania NS-5 pentode. 

In the latter stages of development, some mis- 
siles with launching accelerations near 10,000# 
were encountered. Relaxation of security re- 
quirements was secured and more rugged tubes 
were made by simple mechanical changes. 

In favorable contrast to the oscillator triode 
situation, the allowable ruggedness level for the 
pentode proved sufficient for suppression of 
microphonics. Presumably because of the low 
voltage level at the pentode grid, microphonic 
audio amplifiers were exceedingly rare. In al- 
most every case of a noisy unit, blocking of the 
oscillator would remove all microphonic output. 

Figure 36 show T s the external appearance of 
pentodes of different manufacturers ; Figure 37 
shows the internal construction of a typical 
pentode. 



AMPLIFIER SYSTEMS 


115 


For further details reference should be made 
to the final reports of the tube manufactur- 
ers. 201 ’ 202 


3 .2.5 Adjustment and Testing 

With components of commercial tolerances, 
it was found possible to build the amplifiers 
with only one adjustable component; the in- 
verse feedback condenser, shown, for example, 
as C 8 in Figure 26. This condenser controlled 



Figure 37. View of NS-5 pentode with envelope 
removed, showing various components. 


the peak gain primarily, with only second-order 
effects on the peak frequency. In some of the 
double-peaked amplifiers, an additional adjust- 
ment was provided in the form of a resistor 
controlling the Q of the series resonant circuit 
responsible for the low-frequency peak. 

Testing is described in greater detail in 
Chapter 7. Two properties of the signal injec- 
tion circuit were critical: the impedance and 
the hum level. The impedance of the synthetic 
signal source had to be the same as the actual 
source, since, as was pointed out earlier, this 
impedance is a portion of the feedback voltage 
dividing network. In addition, hum, or a signal 


of power-supply frequency, had to be injected 
along with the desired signal to simulate actual 
operating conditions. This was because milli- 
volts required to fire the thyratron were meas- 
ured rather than voltage gain, since the former 
were of more direct applicability. The effective 
critical bias on the thyratron, however, de- 
pended on the amount and phase of hum voltage 
passed through the amplifier. Special signal in- 
jection circuits were consequently designed for 
each amplifier. 

Where gain was measured, the output volt- 
age was defined as that appearing on the thyra- 
tron grid. In virtue of the feedback applied to 
the amplifier and also of the high-frequency 
attenuating network preceding the thyratron 
grid, the impedance level at this point was very 
high. This necessitated the use of very high- 
impedance voltmeters for the measurement of 
output voltage. 


3 2 6 Response to Spurious Signals 

Spurious signals are here defined as any sig- 
nals due to causes other than motion with re- 
spect to a reflector. Since these latter are 
always expected in a relatively restricted re- 
gion of the frequency spectrum, the first pre- 
caution is evidently to keep amplifier gain low 
outside this region. Certain transients however 
are of sufficient magnitude to require separate 
consideration. 

The rocket fuzes for antiaircraft use gener- 
ally were required to be ready for operation in 
a period ranging from % sec to slightly more 
than 1 sec. During this period, the d-c level at 
the amplifier input changes from 0 to approxi- 
mately — 40 v; filament voltage is applied sud- 
denly to all tubes and plate voltage to all, al- 
though not simultaneously; the application of 
plate voltage to the thyratron is delayed. Firing 
during this cycle is prevented by maintaining 
the following sequence. 

1. Plate and filament voltage to oscillator, 
diode (if any), pentode, and filament voltage 
for the thyratron are applied. Since the pentode 
filament is not yet emitting, its plate assumes 
the potential of the supply voltage and a posi- 
tive pulse appears on the thyratron grid. Since 


SECRET 


116 


ELECTRONIC CONTROL SYSTEMS 


the thyratron filament is also cold and its plate 
circuit is open, firing does not occur. 

2. The properties of the pentode and oscilla- 
tor (and diode, if any) filaments, and the volt- 
ages supplied to them, are so adjusted that the 
oscillator (or oscillator and diode) warm up 
before the pentode. Thus when the pentode 
begins to warm up, the tube is at first cut off by 
the negative surge on its input. Pentode warm- 
up is substantially complete before this nega- 
tive charge leaks off via the grid leak, resulting 
in a smooth drop of the pentode plate to its 
operating point. Thus, during the time the 
thyratron is warming up, a negative signal is 
appearing on its grid. 

3. The only possible transients due to sud- 
den application of thyratron plate voltage are 
the signals due to thyratron plate-grid capaci- 
tance, and any signals due to switch action in 
leakage r-f fields from the oscillator. The first 
is suppressed by the large capacity from thy- 
ratron grid to ground. The second is suppressed 
by associating chokes and capacities with the 
switch in the appropriate fashion. Since leak- 
age fields are small, switch-oscillator coupling 
is not strong and circuit design is not critical. 
(See Section 3.3.) 

A somewhat different problem occurs in the 
case of mortar fuzes. These are sometimes fired 
at very high angles, so that velocities are low 
near the peak of the trajectory. At the conse- 
quent low generator speeds and supply volt- 
ages, the oscillator plate current will be re- 
duced; since plate current is a large factor in 
determining C bias, the thyratron bias will be 
reduced. Additionally, the supply-voltage rise 
with increasing speed on the downward leg of 
the trajectory will be very rapid and may give 
rise to transients within the amplifier itself 
resulting in positive signals on the thyratron 
grid. 

Since thyratron plate voltage is also low at 
low speeds, some reduction in C bias can be 
tolerated. A shunt load on the B supply can be 
used which will draw enough current through 
the bias resistor to hold the thyratron at low- 
plate voltages. 

The only transient on the downward leg of 
the trajectory which gave positive thyratron- 
grid signals was found to be associated with the 


pentode screen-grid circuit. The problem was 
solved by supplying the screen from a voltage 
divider, in place of a simple series dropping 
resistor. Because of the differing screen im- 
pedances of tubes of different make, a different 
divider was used for each tube manufac- 
turer. 

As in the rocket fuze, any transients due to 
the oscillator dropping out of oscillation and 
starting up again were handled by the shorter 
warm-up time of the oscillator filament, com- 
pared to pentode and thyratron filaments. 
Where necessary, this difference was accentu- 
ated by series resistors in pentode and thyra- 
tron filament circuits. 

It is of interest to note the rapidity of warm- 
up achieved with the tubes at hand ; the 
MC-382, for example, was completely stabilized 
and ready for arming (application of thyratron 
plate voltage) in less than 0.25 sec after the 
application of oscillator and amplifier supply 
voltage. 


3,2 7 Tolerance of Components and 
Variation in Performance 

Exhaustive studies of the effects of varia- 
tions in the component values were conducted. 
In general, the conclusion reached was that 
satisfactory restriction of performance varia- 
tions could be achieved in the single-peak am- 
plifiers by the use of unselected components of 
10 per cent tolerance. (In the double peak am- 
plifiers, 5 per cent components were used in the 
feedback network.) By the use of sorting (pair- 
ing high capacities and low resistors, or vice 
versa) 20 per cent components could be used in 
most places. 

Except for a few small resistors (as in fila- 
ment circuits), carbon resistors and paper con- 
densers were employed. The temperature co- 
efficients are opposite but that of the resistors 
dominates, so that the amplifier has a negative 
gain-temperature coefficient. The value depends 
largely on the form of the gain-control con- 
denser, ranging from —0.7 per cent per degree 
centigrade with one form (twisted pair of 
wires) to —0.2 per cent per degree centigrade 
with another (ceramic condenser). 


SECRET 


THE DETONATOR CIRCUIT 


117 


The supply voltage sensitivity was not so 
large as might be expected from a regenerative 
circuit; percentage gain changes were approxi- 
mately equal to percentage supply-voltage 
changes. 

Because of the many high-impedance points 
m the amplifiers, good protection against mois- 
ture was required, including “built-in” mois- 
ture as well as any encountered in subsequent 
exposures to humid atmospheres. The imped- 
ance between pentode grid and plate was par- 
ticularly high ; this necessitated specifying bet- 
ter than common practice in tube washing to 
eliminate any conducting salts or acids on the 
tube press. The assembled amplifier was given 
a dip in hot wax to drive out as much moisture 
as possible and seal it out, after which the as- 
sembly was potted. Tung oil and Glidden pot- 
ting compounds were used. (See Section 4.7.) 

Figure 38 shows the variations encountered 
from all causes in one type of amplifier, except 
supply voltages, which were standardized. Tem- 
perature, of course, was not standardized, but 
the range of variation was limited. 


3 3 THE DETONATOR CIRCUIT f 
General Requirements 

The purpose of any fuze is to initiate the 
high-velocity shock wave needed to set off the 
explosive charge. In the proximity fuze, an 
electric detonator is used to link together the 
operating parts of the fuze and the powder 
train which sets off the high explosive. The de- 
tonator assembly must meet the stringent 
safety requirements of the Armed Forces, and, 
for proper functioning, the detonator imposes 
even more stringent requirements on the elec- 
tric firing network. The detonator is fired by 
the discharge through its bridge wire of the 
energy stored on a large capacitor. A screen- 
grid thyratron is used as the electronic switch 
to discharge the capacitor through the detona- 

f This section was prepared by Charles Ravitsky of 
the Ordnance Development Division of the National 
Bureau of Standards. Mahlon F. Peck of the same 
organization prepared Section 3.3.4 on the properties of 
the thyratron. Major bibliographical references for this 
section are 6, 8, 25, 57, and 58. 


tor. The thyratron holding bias is set so that 
the tube will fire when the fuze receives a sig- 
nal larger than the predetermined threshold for 
functioning. In order that the fuze will not 
function prematurely, both electric and me- 
chanical methods are used to make the fuze en- 
tirely inoperable before arming. Before elec- 
tric arming occurs the detonator bridge wire is 
not connected to the electric circuit, so that no 
current can flow through it, regardless of what 
happens to the rest of the fuze. Further, in the 
generator-powered fuzes no power is available 








4 



A 







/ 



A\ 






// 

/ 



\\\ 





/ 





A\ 




/ 

/ 4 

' 




W\ 




A 






Au 



J 

/y 

'/ 






\W 


/> 
/ / 

z 7 

y 







\V\ 

/ 

/) 
/ / 

// 

/ 








'V 

\\\ 

^ 

/ 








vy 

w 

\ 

^ 


20 30 40 50 60 70 80 90 100 200 

FREQUENCY (CPS) 


Figure 38. Variations of gain encountered in 
feedback amplifier. Voltages were held constant 
and gain curves translated to common peak fre- 
quency. Dotted curves represent limits within 
which are included characteristics of approxi- 
mately % of the amplifiers. 


until the fuze is traveling through the air at a 
speed greater than 80 mph (see Section 3.4). 
As an additional protection, before mechanical 
arming, a ^4-in. thick brass plate is located be- 
tween the detonator and the tetryl powder train 
(see Chapter 4). Thus, even if the detonator 
explodes, the resultant shock wave, after pass- 
ing through the brass plate, will not be large 
enough to set off the tetryl. 

It is obvious that the detonator itself must 
be so located that the shock wave due to its de- 
tonation will set off the tetryl booster charge. 
This limitation permits either the end or a side 
of the metal cup to face the tetryl. It is not so 


SECRET 


118 


ELECTRONIC CONTROL SYSTEMS 


obvious, however, that the electric components 
of the detonator circuit must be so arranged 
that stray coupling to the other electric net- 
works is minimized. It was found that inade- 
quate shielding of the detonator circuit some- 
times caused early functioning of the fuze due 
to transients set up at the time of arming. In 
order to eliminate the detrimental effect of 
transients when the detonator was connected 
to the circuit at arming, r-f chokes were put 
in series with the detonator, and a condenser 
was used to by-pass it at radio frequencies 
(compare with Section 3.1.5). 

The principal components of the detonator 
circuit are the electric detonator, the condenser, 
and the thyratron (Figure 39). In addition, the 
impedance of the filament power supply is in 
series with one leg of the thyratron filament in 
some of the fuzes, and half the impedance is in 
series with each leg of the thyratron filament in 



Figure 39. Elementary detonator circuit. 


other fuzes. Also, in some of the fuzes there is 
an r-f choke 172 in series with each of the det- 
onator leads and a small condenser in parallel 
with the detonator. These additional compo- 
nents have only a minor effect on the proper 
operation of the detonator circuit and were 
added to reduce transients at arming. A small 
resistor of 3 or 5 ohms is included in series 
with the ungrounded end of the thyratron fila- 
ment in order to decrease the filament current 
to the value for which the filament was de- 
signed. 

This section of the report will deal with the 


major components of the detonator circuit. As 
the other components do not appreciably influ- 
ence the action of the circuit, they can be dis- 
posed of here in only a few words. The filament 
resistance is a commercial 1,4 -w resistor. The 
r-f choke in series with the detonator is the 
same as those used in the oscillator section of 
the fuze. It consists of 78 turns of No. 38 enam- 
eled wire, wound on a core the size of a *4-w 
resistor. The shunting condenser used in the 
T-82 is a 500 p|if Ceramicon condenser. The 
impedance of the filament power supply is dis- 
cussed in Section 3.4 on the fuze power supply, 
which covers both batteries and generators. 


The Detonator 

The detonator, as the connection between the 
fuze and the high explosive, is a critical part of 
the fuze. In order for manufacture of the fuze 
to be possible, the characteristics of the various 
fuze elements must be such that they can meet 
the requirements of the other components. The 
initial requirement is imposed by the high ex- 
plosive [HE] used in the missile. In order to set 
off the HE the Army Ordnance Department re- 
quired 212 the use of a tetryl (trinitrophenyl- 
methylnitramine) booster. To assure a high- 
order detonation the Ordnance Department 
specified that the tetryl powder train should 
ample safety factor. The inner diameter of the 
HE, and a length of 0.75 in. will allow an 
ample safety factor. The inner diameter of the 
tetryl cup may be as little as 0.375 in. with no 
apparent diminution in the velocity of the 
shock wave. With the tetryl powder train speci- 
fied by the Army, the problem arose of procur- 
ing an electric detonator which could initiate 
a high-order detonation in the tetryl, and which 
would not impose too severe requirements on 
the electric components. 

Many squibs, detonators, blasting caps, and 
semicaps which were commercially available 
were tried, as well as an experimental high- 
impedance high-voltage detonator. For the ini- 
tial fuze testing, the ND-5, a fast violent but 
poor flame-throwing squib made by the Hercules 
Powder Company, was used. This company 
then developed the ND-24 for use in these fuzes, 


THE DETONATOR CIRCUIT 


119 


as an improvement over the ND-5, Although it 
functioned satisfactorily in the field tests, in 
which it was used to set off a potassium per- 
manganate or a black powder spotting charge 
(cf. Chapter 8), it was not powerful enough 
to insure detonation of the tetryl booster. It 
therefore had to be abandoned. Hercules then 
developed a satisfactory detonator, which was 
known successively as the BS-4 or BS-5; the 
Detonator, Electric, T-3; the Detonator, Elec- 
tric, M-2; and finally the Detonator, Electric, 
M-36. The latter three designations are official 
Army Ordnance nomenclature and indicate ac- 
ceptance for use, first as an experimental item 
and then as a standard Army production item. 

The M-2 electric detonator 212 (see Figure 
40) itself consists of a three-element powder 
train. The bridge (heater) wire is embedded in 
about 0.2 g of mercury fulminate, which is fol- 
lowed by a primer charge of 0.13 ± 0.02 g of 
lead azide, which in turn detonates the base 
charge of 0.14 ± 0.02 g of pentaerythrite tetra- 


Figure 40. M-2 detonator used in radio prox- 

imity fuzes. This detonator was also designated 
BS-4 and M-36. 

nitrate [PETN]. This construction permits a 
very compact assembly for the explosive pow- 
der train leading to the tetryl booster charge. 
The bridge wire, when heated electrically, sup- 
plies the energy to ignite the mercury fulmi- 
nate and thus initiates the explosion. The 
heater wire is made of Nichrome and is ini- 
tially 0.09 ± 0.01 in. long and is 0.00050 ± 
0.00005 in. in diameter. In connecting the Ni- 
chrome wire to the copper lead wires, solder is 
dropped over the ends, so that only about half 
its length is effective in heating the mercury 
fulminate. The specified resistance for the deto- 
nator is 9 ± 3 ohms, allowing a 100 per cent 
variation between the minimum and maximum 
resistances and therefore between the mini- 
mum and maximum effective lengths. 

Time Lags. As the fuzes are used on projec- 
tiles traveling at high speeds, any time lag be- 


tween the operation of the fuze and the explo- 
sion of the HE must be quite small. The delay 
inherent in the detonator may be broken down 
into three components : the time it takes for the 
incident electric energy to heat the Nichrome 
wire, the transfer of enough heat energy to 
ignite the mercury fulminate, and the explosion 
of the PETN base charge, which detonates the 
tetryl booster. 

In operation, enough heat is generated in the 
bridge wire to melt it by the dissipation of over 
1 millijoule of energy in it within 1 msec. 57 
Nichrome melts at 1350 C, so that the grains of 
mercury fulminate adjacent to the bridge wire 
become immersed in a metallic bath at that 
temperature. The time between the liquefaction 
of the bridge wire and the explosion of the 
PETN is less than 0.2 msec. The Nichrome wire 
heats about 4 micrograms of mercury fulminate 
to its ignition temperature to start the explo- 
sion, which is thus initiated within a cylindrical 
layer about 0.00045 in. thick around the 
0.00025-in. radius Nichrome wire. 57 The explo- 
sive wave travels through the tetryl booster 
after its initiation by the PETN, at over 7,000 
m per sec, so that the time lag in the booster is 
less than 5 psec. The time delay in the explo- 
sive elements is thus quite small. The overall 
time delay in the detonator is, however, influ- 
enced by the rate at which electric energy is 
dissipated in the Nichrome heater wire. If this 
rate is less than 70 mw, 57 - 173 the heat produced 
will be conducted away through the detonator 
without igniting the mercury fulminate. In 
order to fire the detonator, energy must be sup- 
plied at a rate faster than it can be safely con- 
ducted away. The greater the energy dissipa- 
tion is above this lower limit, the smaller the 
time delay. Further, in order to waste as little 
energy as possible in heat conduction, the total 
energy should be supplied in as short a time as 
possible. Thus, a constant energy dissipation of 
1 w will fire the detonator in 1 msec. However, 
because of the thermal inertia of the mercury 
fulminate in contact with the Nichrome heater, 
energy dissipation at the rate of 25 w is re- 
quired to decrease the total time to 170 psec. 

As a fuze may be used in the upper atmos- 
phere, where the temperature is far below 
freezing, the possible effect of low tempera- 


] SECRET \ 





120 


ELECTRONIC CONTROL SYSTEMS 


tures on the action of the detonator is impor- 
tant. The only measurable effect was that more 
energy was required for detonation at lower 
temperatures. This effect had been anticipated, 
but even at —78 C only about 10 per cent more 
energy was required. 166 

Leakage Resistance. Another characteristic 
of interest is the resistance between the detona- 
tor lead wires and its metal shell. This property 
is important because of the possible firing of 
the detonator by a voltage between the case and 
one lead or by leakage otherwise affecting the 
proper operation of the detonator circuit. The 
minimum resistance measured in a group of 
fifty detonators at ordinary temperature and 
humidity was 50,000 megohms. When subjected 
to a relative humidity of 95 per cent for 24 
hours, the lowest resistance decreased to 12,000 
megohms. 24 The effect of leakage resistances of 
these magnitudes upon the proper operation of 
the detonator circuit can be neglected. 

Specifications. A summary of the pertinent 
operational characteristics of the detonator is 
given in the specification 212 which was used by 
the Army for large-scale procurement. An ex- 
tract follows. 

The detonator shall function in an elapsed time not 
exceeding 0.005 second with an electrical current of not 
more than 0.175 ampere at 20°C, or with an electrical 
current of not more than 0.225 ampere at — 15°C. 
Eighty per cent or more of the detonators shall also 
function in an elapsed time not exceeding 0.001 second, 
and none over 0.003 second with the discharge from a 
condenser of not more than 0.7 microfarad capacitance, 
charged from a battery of not more than 75 volts 
potential. 

Some lots of detonators have had difficulty 
in passing the 0.175-amp specification, which 
is more severe than the other two ; conse- 
quently, a recommendation that this current be 
raised to 0.200 amp was made. 


The Detonator Capacitor 

The capacitor is used in the detonator circuit 
as a very low impedance power source, which 
must store enough energy to fire the detonator. 
As far as the capacitor is concerned, the opera- 
tion of the thyratron shorts a low resistance, 
on the order of 18 ohms, across it. With the 


minimum supply voltage specified as 125 v, the 
nominal capacitance required to insure that the 
detonator fires is 1 pf. A major requirement for 
the capacitor is that it must be small enough 
so that it does not occupy a disproportionate 
amount of the very limited space in the fuze. 
Although electrolytic condensers easily meet 
the space requirements, they were rejected at 
an early stage in the fuze development because 
of their many faults. 217 They deteriorate during 
storage and then require a long forming period, 
during which they pass excessive leakage cur- 
rent and store very little energy. They cannot 
withstand either low temperatures at high alti- 
tudes, or high temperatures of the tropics. In 
addition, all the energy stored in the electro- 
static field is not immediately released, when 
the capacitor is shorted, because of dielectric 
hysteresis in the condenser. Paper condensers 
are therefore used as being the most efficient 
space utilizers which do not have these faults. 
In order to eliminate the deleterious effect of 
high-humidity conditions, the firing condenser 
is metal-clad. 

In all the generator-powered fuzes, except 
those which use RC plate arming, the detonator 
firing condenser also serves as the part of the 
filter circuit of the power supply. The charac- 
teristics which determine its effectiveness in 
firing detonators are its capacitance, induct- 
ance, and internal series resistance. The dielec- 
tric absorption of a paper condenser is negli- 
gible for a single discharge. The leakage re- 
sistance is of only minor importance in a unit 
which does not use RC arming, as long as it is 
not so low that it presents an appreciable 
pow T er drain on the generator. A 5-megohm 
leakage resistance will cause negligible drain on 
the power supply. 

The series resistance and the inductance of 
the detonator firing capacitor are not measured 
separately ; instead, a surge current test is 
made, which is intended to determine how well 
the capacitor will discharge through the deto- 
nator and thyratron. The capacitor is charged 
up to 135 v and then discharged through a 
15-ohm resistor. The peak current is required 
to be 7 amp. As either inductance or series re- 
sistance in the condenser would lower the peak 
current, this test gives an indication of the 


SECRET 


THE DETONATOR CIRCUIT 


121 


combined effect of both. Furthermore, as the 
condenser is actually used this way, the test is 
quite valid. 

When measuring the peak surge current by 
discharging the condenser through the 15-ohm 
resistor, the impedance of the switch is in 
series with the resistor. The spark that occurs 
as the switch is closed represents a variable 
impedance which limits the peak surge current. 
It is, therefore, necessary to use a fast-acting 
mercury switch, rather than an ordinary 
switch. 

The 7-amp limit was chosen because the bet- 
ter capacitors were able to pass this test, and 
the requirement allows a 100 per cent factor of 
safety in firing the detonator. In Figure 41 is 
shown the diminution in the peak surge cur- 



Figure 41. Effect of series inductance on peak 
surge current of detonator firing capacitor. 


rent, due to the series inductance, when the 
1.5 pf condenser used in the battery-powered 
fuzes is tested. As the time lag is also of in- 
terest, Figure 42 gives the time to peak current 
as a function of the inductance. 

The possible effect of the inductance in de- 
creasing the energy dissipated in the resistive 
component of the circuit was investigated. In 
the actual circuit, the thyratron stops conduct- 
ing when its potential difference falls below 
about 20 v. The energy dissipated in the 15-ohm 
resistor was, therefore, determined as a func- 
tion of the inductance for a 1.5 pf capacitor dis- 
charging from 135 to 20 v. Figure 43 shows that 
even a 100-ph inductance would decrease the 
energy dissipation less than 2 per cent. Thus, a 
capacitor would have to be quite poor for its as- 


sociated inductance to have an appreciable ef- 
fect. As shown in Figure 41, with so large a 
value of inductance the condenser would cause a 
peak current of less than 7 amp, and would, 
therefore, fail the peak surge current test. An 



Figure 42. Effect of series inductance on time 
to peak surge current of the detonator firing 
capacitor. 


inductance of 100 ph would decrease the peak 
surge current to 6.4 amp. The effect of the in- 
ductance on changing the time for the energy 
discharge is negligible. As shown in Figure 44, 
the time varies from 43 to 38 psec as the induct- 
ance increases from 0 up to 100 ph. 

The characteristics of capacitors may be 
affected by the ambient temperature and hu- 
midity, so that these factors must be taken into 



INDUCTANCE (HENRIES) 

Figure 43. Effect of series inductance (asso- 
ciated with detonator firing capacitor) on energy 
dissipated in resistance load. 

account. 166 The principal effect of a high rela- 
tive humidity is to decrease the leakage resist- 
ance of the capacitor. It was found necessary 
to use metal-cased condensers in order to elimi- 



122 


ELECTRONIC CONTROL SYSTEMS 


nate this difficulty. Temperature variations 
affect both the capacitance and the leakage re- 
sistance of the condenser. At low temperatures 
the leakage resistance increases; at high tem- 
peratures it decreases, showing that the dielec- 
tric and the impregnating material have high 
negative temperature coefficients of resistivity, 
as might be expected. The capacitance de- 
creases at low temperatures, so the condensers 
used must pass the specifications at the lowest 
operating temperature for the fuze. Moreover, 
it is well known that both the capacitance and 
leakage resistance change as a result of a tem- 
perature cycle. 217 Therefore, in order to deter- 
mine how the condensers will react to different 



Figure 44. Effect of series inductance on time 
of capacitor discharge. 


weather conditions, they must be temperature- 
cycled several times. Data are taken during 
each cycle, and the capacity and leakage resist- 
ance are required to meet the specifications 
throughout. Fairly large samples must be used 
in these tests in order that the data represent 
the condenser type, rather than just the sam- 
ples tested. Another characteristic that is de- 
termined during these temperature and hu- 
midity tests relates to the mechanical strength 
of the condenser assembly, particularly to as- 
sure that the leads do not come out of the con- 
denser. The temperature and humidity condi- 
tions do not affect the operations of the con- 
denser in the peak surge current test. This is 


as expected, since the peak surge current is in- 
dependent both of the capacity and of the leak- 
age resistance if it is greater than 1,000 ohms. 


The Thyratron 

The thyratron is used in the variable-time 
[VT] fuze as an extremely sensitive electronic 
switch. Rather stringent requirements are 
placed on the thyratron by the physical size of 
the fuze, the available power supply, the char- 
acteristics of the oscillator and amplifier sec- 
tions, the detonator, and discharge condenser, 
and the use to which the fuze is put. 

Because of the limited volume of the fuze, it 
was necessary to develop a thyratron 8 occupy- 
ing not more than % cu in. of space. Into this 
space were fitted the components required to 
give the thyratron the electric characteristics 
required by the factors noted above. These re- 
quirements were established as follows : 

Low Power Consumption. In both battery 
and generator powered fuzes the available 
power is distinctly limited. (See Section 3.4.) 
It was, therefore, necessary to design the fila- 
ment for the lowest possible power consump- 
tion consistent with the required life and surge 
characteristics of the tube. 

Critical Grid Voltage. An allowable range of 
—2.1 ± 0.4 v for critical grid voltages was dic- 
tated by the amount of bias voltage which 
could be incorporated in the battery and the 
available signal level from the oscillator-ampli- 
fier section of the fuze. 

Effective Critical Grid Voltage. The value 
for critical grid voltage defined above is for d-c 
operation. When the thyratron filament is pow- 
ered by alternating current the critical grid 
voltage is increased because the filament poten- 
tial is negative during half of each cycle, and 
the critical grid voltage is referred to the most 
negative portion of the filament. As installed in 
a fuze circuit the thyratron grid receives tran- 
sient and ripple signals from the amplifier. The 
phase of the ripple signal is usually such as to 
reduce the effect of a-c ripple on the thyratron 
filament. The highest negative bias at which 
the thyratron will fire, under operating condi- 
tions, is called the effective critical grid voltage. 


SECRET 


THE DETONATOR CIRCUIT 


123 


Stability. Supply voltages of generator-pow- 
ered fuzes are generally higher than those pow- 
ered by batteries. In addition, the battery volt- 
ages change considerably with age and climatic 
conditions. These factors necessitated a thyra- 
tron whose critical grid voltage was as insensi- 
tive as possible to changes in operating voltage 
both from the standpoint of magnitude and the 
ability of the grid to maintain control. 

Surge Characteristics. The properties of the 
detonator and discharge condenser, together 
with the nature of the fuze application, deter- 
mined the required surge characteristics. The 
thyratron must be able to pass peak surge cur- 
rents of the order of 7 amp in 0.001 sec after 
triggering, in order to transmit the energy 
from the discharge condenser to the detonator 
in a time short enough to set up a high-order 
detonation at the same point in space at which 
the triggering signal was received, the speed of 
missile being approximately 1,000 to 1,500 fps. 

Leakage and Grid Current. Both leakage be- 
tween plate and grid and grid current contribute 
to unstable critical grid voltages and therefore 
must be minimized. Where RC arming is used 
in addition to mechanical arming, leakage be- 
tween plate and filament is important and must 
also be minimized. 

Microphonics. Because of the multitudinous 
vibrations and shocks to which the tube is sub- 
jected in operation it was necessary to have the 
thyratron mechanically strong, so that it would 
not operate prematurely. 

Life. Although the fuze itself needs to oper- 
ate only once, a certain amount of testing is 
required prior to use. Since it appeared that 
one way to obtain all the required electric char- 
acteristics in so small a tube was to sacrifice 
greatly in the time of useful operation, it was 
necessary to preserve sufficient reserve to guar- 
antee proper operation after the testing. Fur- 
ther limitations are discussed in Section 3.1.4. 

The first step in obtaining a suitable thyra- 
tron was to examine the existing types of small 
tubes. Tests were made on the Bell Telephone 
Laboratories type 1278 GY-2 (see Figure 45), 
the General Electric miniature thyratron and 
the Sylvania type SN-738. 6 The 1278 GY-2 was 
soon eliminated as a possibility for several rea- 
sons. Although the critical grid voltage of this 


type was too high and spread over too great a 
range, the principal objection was the manner 
of construction of the tube itself. The geometry 
of the tube was such as to make it susceptible 
to external fields, making it impossible to use 
the tube in closely packed assemblies without 
careful external shielding. This was undesir- 
able because of the premium on space. 

The GE miniature thyratron 8 had the dis- 
advantages of excessive size, susceptibility to 
external leakage caused by handling, and a 
limitation of the number of times it could be 
surged. Because of its manner of construction, 
it had a distinct advantage in that the critical 
grid voltage could be very closely controlled, 
both as to magnitude and stability. It was, 
therefore, decided that the size should be re- 
duced and an attempt made to reduce the sus- 
ceptibility to leakage and improve the surge 
characteristics. 

The Sylvania SN-738 had been developed for 
Section T and, in general, was found to have 
the proper characteristics with the exception 
that it was designed to operate at low voltage 
and exhibited poor performance at the higher 
voltages used in Division 4 fuzes. It was de- 
cided that this tube should be redesigned to 
operate at the higher voltages and also to elimi- 
nate certain classified features peculiar to the 
original purpose for which it was designed. 

The redesigned GE and Sylvania thyratrons 
were known as the microthyratron and SA-782 
respectively (see Figure 45). The microthyra- 
tron preserved all the advantages of close grid 
control found in the miniature thyratron and 
largely eliminated the problem of leakage by 
virtue of a special lacquer coating over the sur- 
face of the tube. The microthyratron is essen- 
tially a cold cathode tube, having a filament 
supplying only enough emission to initiate the 
discharge which immediately transfers to an 
anodized aluminum spotting tab. This tube was 
finally abandoned, because it was not possible 
to maintain the filament emission at the proper 
value over the range of filament voltages to 
which the tube was subjected, nor was it pos- 
sible to obtain a spotting tab which would stand 
the punishment of repeated surging of the 
thyratron. 

The Sylvania thyratron in its final form as 


124 


ELECTRONIC CONTROL SYSTEMS 


the SA-782B (shown in breakdown in Figure 
46), meets all of the requirements outlined 
above. The outstanding features in the design 
of this tube were the introduction of an addi- 



Figure 45. Various thyratrons developed and 
considered for use in radio proximity fuzes. 
From left to right they are : GE microthyratron, 
BTL 1278 GY-2, GE version of Sylvania 

thyratron, and Sylvania SA-782B. The latter 
tube was also known by the NDRC designation 
NS-4 and the Signal Corps designation 2D29. 


tional grid between the control grid and the 
anode and an auxiliary shield around the fila- 
ment above the top mica. The additional grid 
is connected to the negative leg of the filament 
and makes possible a lower critical grid voltage 
than is otherwise consistent with the geometry 
of the tube and also controls the spread of criti- 
cal grid voltage from tube to tube. The auxil- 
iary shield is connected to the control grid and 
makes stable operation possible at higher than 
normal voltages. This shield was necessitated 
by the fact that the emitting portion of the fila- 
ment sometimes extends above the top mica 
and at sufficiently high anode voltages causes 
an arc-over to the anode because of the ab- 
sence of grid control in that part of the 
tube. 8, 67, 189, 202, 213 


Circuit Operation 

The sequence of operations in the fuze after 
the projectile is released is such that it can 
function as soon as arming is completed. Upon 
release the generator propeller starts to turn, 
and it reaches the equilibrium rotational veloc- 
ity, due to its speed through the air, in 5 to 6 


revolutions. The tube filaments warm up with- 
in 0.4 sec, 11 and both oscillator and amplifier 
are in operation. The B voltage has already 
reached its steady-state value. However, the 
fuze cannot function, because the electric deto- 
nator is not yet connected to the firing circuit. 
The details of mechanical arming are covered 
in Chapter 4 ; here it will suffice to state that a 
preset number of turns of the fuze propeller is 
required before the detonator makes electric 
contact. Until this time, the detonator is sepa- 
rated from the tetryl booster by a %- in. thick 
brass plate. Upon arming, the detonator bridge 
wire is connected between the detonator firing 
condenser and the thyratron plate. Except 
when using RC arming (see Section 3.3.6), the 
firing condenser is also the output filter con- 
denser and is already charged up to the operat- 
ing potential of about 140 v. At electric arm- 
ing, therefore, a 140-v positive pulse is applied 
to the thyratron plate. A part of this arming 
pulse appears on the thyratron grid in the ratio 

f n 



Figure 46. Breakdown of thyratron showing 
electrode SA-782B structure. 

of the grid-to-filament impedance to plate-to- 
grid impedance. In order to prevent this grid 
pulse from firing the thyratron, the grid-to-fila- 
ment impedance is reduced by connecting a con- 
denser from grid to ground (shown in Figure 
39). In the early fuzes a 50-qpf condenser was 
used and was quite satisfactory. In later pro- 
duction fuzes, when a 500-ppf condenser was 
used in order to get proper amplifier shaping, 




THE DETONATOR CIRCUIT 


125 


an additional safety factor was provided. The 
presence of this arming pulse places an addi- 
tional requirement on the thyratron; the leak- 
age resistance from the plate to the grid must 
be quite large, on the order of 1,000 megohms. 
At any time after arming, a sufficiently large 
signal, 3 to 4 v positive, impressed on the thyra- 
tron grid by the amplifier, will fire the thyra- 
tron ; and the condenser will discharge through 
the tube and the detonator, initiating the ex- 
plosion. 

Just as there is a time lag for a signal to 
travel through the amplifier, 54 so there is a time 
lag between the incidence of the firing signal 
at the thyratron grid and the explosion of the 
detonator. 25 This time lag is on the order of 
1 msec and is almost entirely due to the de- 
tonator. The delay due to the thyratron is usu- 
ally less than 150 psec 189 and that due to the 
condenser is less than 60 psec. One millijoule 
of energy dissipated in the detonator in 1 msec 
will set it off ; in order to decrease this time 
lag, it is necessary to dissipate more energy, 
faster, in the detonator. For example, this time 
delay can be reduced to 200 psec by dissipating 
3.6 milli joules in it in this time. 58 

Component Values. To determine the effi- 
ciency of a given capacitance in firing a de- 
tonator, a condenser of the given size is used to 
fire detonators through thyratrons in the deto- 
nator circuit. The condenser potential is ini- 
tially too low to fire the detonator when the 
thyratron fires, and it is gradually increased 
until the detonator does function. 25 By using 
several thyratrons, detonators, and condensers, 
the spread in firing voltage due to variations in 
these components is determined. These data are 
important to determine the minimum capaci- 
tance that may be used to fire the detonator. 

Tests were made on the detonator circuit, 
with all components, beyond the extreme tem- 
perature limits foreseen for actual operation, 
namely, —78 C and 60 C, to determine the 
effects of extreme temperatures. The power 
supply specifications permit a minimum B volt- 
age of 125 v under normal conditions ; however, 
at low temperature the efficiency of the sele- 
nium-button rectifier assembly decreases. At 
—40 C, the normal output of 135 v will be only 
106 v 1 sec after launching, 69 at which time a 


rocket fuze should be ready to function. This B 
voltage was used in some of the tests, as was 
the minimum expected A voltage, 1.17 v rms. 178 
The filament series resistor lowered the thyra- 
tron filament voltage still further. It should be 
noted that this lowered filament voltage actu- 
ally has a beneficial effect. Although the de- 
creased filament emission increases the thyra- 
tron time delay, this time is still sufficiently 
small. In addition, because of the lower fila- 
ment operating temperature, the filament re- 
sistance is lower. This decreased series resist- 
ance permits a larger fraction of the condenser 
energy to be dissipated in the detonator. After 
making allowances for all the other factors 
which influence the operation of the detonator 
circuit, it was found that the minimum capaci- 
tance which would fire any good detonator, 
using any thyratron which passed the tube 
tests, was 0.96 pf. 58 It became apparent in these 
tests that the largest single variable in deter- 
mining the firing capacitance and voltage needed 
was the thyratron, although all the tubes used 
had passed the tube tests. 

The thyratron is used as a low-impedance 
switch to permit the energy stored in the con- 
denser to be dissipated in the detonator. About 
40 per cent of the condenser energy is actually 
transferred to the detonator. 6 

The minimum capacitance value can be fur- 
ther lowered by a selection test for thyratrons 58 
(this technique was not used in production). 
Such a test measures the efficiency of the thyra- 
tron in permitting energy transfer. Rejection 
of less than 5 per cent of the thyratrons which 
pass the thyratron specification tests would 
lower the minimum value of the thyratron- 
firing capacitor to 0.87 pf. With further divi- 
sion of the tubes into two approximately equal 
groups, the better group would permit the use 
of an 0.5 pf firing capacitor in fuzes where the 
space requirements are critical. The other 
group of thyratrons could be used in the larger 
fuzes, where the space requirements are not so 
stringent. 58 

3,3 6 Electric (RC) Arming 

The use of a resistance-capacitor network to 
delay arming provides a delay in electric arm- 


SECRET 


126 


ELECTRONIC CONTROL SYSTEMS 


ing (RC) after mechanical arming has oc- 
curred. 58 It consists of placing a large resistor, 
on the order of a megohm, between the single 
filter capacitor used with RC arming and the 
detonator firing capacitor. At mechanical arm- 
ing the detonator firing capacitor starts 
charging. The fuze cannot function until the 
capacitor potential is high enough to set off the 
detonator if the thyratron should fire. The de- 
tonator firing capacitor and the arming resistor 
are shorted by a large resistor, so that there is 
no charge on the capacitor before mechanical 
arming occurs. 181 A diagram of the circuit as 
used in the T-171 is shown in Figure 47. The 
time delay before electric arming is propor- 
tional to the size of the arming resistor. Time 
delays up to approximately 8 sec can be 



Figure 47. RC arming circuit of T-171. 


achieved by proper choice of the resistance. An 
upper limit is set by the leakage resistance of 
the capacitor, 163 in comparison with the series 
resistor used. Also of importance is the accom- 
panying elimination of the arming pulse when 
RC arming is used. 

The data on the potential necessary on a par- 
ticular capacitance to fire the detonator are of 
primary importance when RC arming is used, 
since they permit the calculation of the time 
interval between mechanical arming and elec- 
tric arming. 56 This period is the time taken for 
the capacitance to charge to the firing voltage, 
and it is a function of the supply voltage, the 
capacitance, the arming resistance, and of the 


particular thyratron and detonator. In making 
arming calculations, the median voltage re- 
quired to fire a detonator through a thyratron 
using a particular capacitance is used, rather 
than the average voltage. The median voltage 
is the voltage which will fire half the detona- 
tors, and it represents the firing data much bet- 
ter than does the average voltage, which is 
unduly influenced by extreme values due to 
atypical components. The data on firing detona- 
tors using different capacitances are summar- 
ized in the following table. 


Median voltage required to fire detonator. 
Capacitance Median voltage 


0.3 

0.37 

0.5 

0.75 

1.0 

1.335 

1.555 

1.7 


96.5 

93.5 

84.0 

74.0 
69.2 

63.0 

60.0 
59.0 


The above values are plotted in Figure 48 as 
the simplest method of averaging all the data, 
as well as permitting determination of the 
median voltages required for capacitances not 
used in the tests. 

Another method for averaging the data is to 
fit a least squares curve to the points on the 
graph, with the added advantage of permitting 
algebraic computations with the resultant equa- 
tion. As the data are the voltages required for 
various capacitances to fire the median det- 
onator, just enough energy is dissipated in the 
detonator to fire it. The least squares curve, 
therefore, indicates a constant energy dissipa- 
tion in the resistive portion of the detonator 
circuit. It also shows the condenser potential at 
detonation to be very nearly equal to the con- 
stant voltage drop V f of both the gas in the 
thyratron when it is conducting and the contact 
potentials in the tube. 

The condenser, initially charged to a poten- 
tial V, stores an amount of energy 


Wi = \CV\ (33) 


After detonation, the residual energy on the 
condenser is 


W f = iCV /. (34) 

After the thyratron starts conducting, before 
the arc starts, the condenser potential drops to 


THE DETONATOR CIRCUIT 


127 


V a , and the energy loss, almost all of which is 
dissipated across the gas in the tube, is 

W a = \CV 2 - iCV a 2 . (35) 

From the initiation of the arc to its extinction, 
the constant potential V p due to both the tube 
contact potentials and the gas, causes an energy 
loss of 

W t = QV f = ( CV a - CV f ) V f . (36) 

The energy dissipated in the resistive portion 
of the circuit is 

W = Wi - Wf - Wa - Wtt 

W = iCV 2 - \CV S 2 - iC(V 2 - Va 2 ) 

- (77,(7* - Vf). (37) 

Solving, 

W = \C {V a - V f ) 2 . (38) 

As the experimental datum is V, 

W = \C{V - V + 7* - V f ) 2 , 
or 

W = J C[V - (V - 7* + V f )] 2 . (39) 

The least squares fit of this equation gives val- 
ues of W = 0.67 millijoule, and V — V a + V f = 
31.6 v. V f is about 18 v, so that V — V a , = 13.6 v, 
which is approximately the condenser potential 
drop before the thyratron arc strikes. This 
value has been verified by oscilloscope measure- 
ments. 58 As both these voltage drops are due to 
the thyratron, the equation may be rewritten, 
W = YzCiV — V t ) 2 . The current during the ini- 
tial 13.6-v drop is comparatively small, and 
most of this energy is dissipated in the tube in 
starting the arc with only a negligible amount 
of it dissipated in the detonator. It should be 
noted that any energy stored in the magnetic 
field of the circuit inductance at peak current 
has been dissipated in the resistive portion of 
the circuit by the time conduction stops. 

Several points from equation (39) are 
plotted as the circles in Figure 48 using the 
above value for the bracket term, but the com- 
plete graph was not drawn because it is almost 
indistinguishable from the curve drawn 
through the experimental points. The excellent 
fit to the eight experimental points, using a 
two-parameter equation, validates the form of 
the equation as being the type to which the data 


conform. As this equation is approximately a 
straight line on log-log graph paper, the ex- 
perimental points were plotted on such paper 
as in Figure 49. The curve which fits them best 
is the straight line drawn through them. The 
points from the theoretical curve are also 
plotted in Figure 49. 

Using the experimental data for the median 
voltages to fire detonators through thyratrons 
with various capacitances and assuming an av- 
erage unit B supply of 140 v, the equation 



Figure 48. Median values of voltage on ca- 
pacitors necessary to fire detonators through 
thyratrons for various values of capacitance. 


t/R — —C In (1 — V/V 0 ) was solved for a 
value of t/R to correspond to each pair of 
capacitance and firing voltage values. 58 The t in 
this equation is the time delay in charging a 
capacitance C to a voltage V through a resist- 
ance R, using a supply voltage 7 0 . These points, 
which represent data for 250 thyratrons, are 
plotted in Figure 50, where the time in seconds 
divided by the resistance in megohms is plotted 
against the capacitance in microfarads. This 
curve can be used to determine the median elec- 
tric arming time in fuzes using RC arming for 
any resistance value, and the curve extends be- 


-SECRET 


128 


ELECTRONIC CONTROL SYSTEMS 


yond the values of capacitance that have been 
used in the fuzes to date. 

The spread in arming times around the 
median values due to variations in the compo- 
nents has been represented in Figure 51, which 
can be used to find the actual time in which a 
given percentage of the fuzes with a certain 
median arming time will be electrically 
armed. 36 In making the calculations, it was 
assumed that both the resistors and the con- 
densers were within 10 per cent of their nomi- 
nal values, with every value in this range 
equally probable. The supply voltage was as- 
sumed to vary between 125 and 160 v in a para- 
bolic probability distribution, with the center 
value three times as likely as the extreme val- 
ues. The distribution of detonator firing volt- 
ages, using a given capacitance, was experi- 
mentally determined, using many thyratrons 



CAPACITANCE (MICROFARADS) 

Figure 49. Median values of voltage on ca- 
pacitors necessary to fire detonators through 
thyratrons for various values of capacitance on 
log-log scale. 

and detonators. It was also assumed that the 
leakage resistance of the condenser was high 
enough so that it would not affect the condenser 
potential appreciably. This assumption requires 
that the leakage resistance be greater than 40 
megohms when a 2-megohm arming resistor is 
used, and greater than 25 megohms when a 
1-megohm arming resistor is used. 163 As previ- 


ously noted, the thyratron is responsible for 
most of the spread in arming time. 

Dumping. The use of RC arming is of de- 
cided advantage when the tactical use of the 



Figure 50. Median arming time in RC circuits 
as related to resistance and capacitance values. 


fuze is such that spurious signals of firing mag- 
nitude are possible shortly after mechanical 
arming. 84 For example, as used on rockets, the 
phenomenon known as afterburning, whereby, 
after the main burning of the propellant is 
over, additional slivers of propellant ignite ; 
the rocket expels quantities of luminous gas 
and produces several random, intermittent sig- 
nals of several times firing magnitude. With 
RC arming, 58 if a firing signal is impressed on 
the thyratron grid before the plate potential 
has reached about 38 v, a low-current discharge 
will start through the thyratron, gradually dis- 
charging the detonator firing condenser. When 
the signal is over, the thyratron grid regains 
control of the tube, the discharge stops, and 
the condenser starts to charge up again. If the 
firing signal occurs after the thyratron plate 
potential has exceeded 38 v but before the con- 
denser has stored enough energy to fire the 
particular detonator through the particular 
thyratron, an arc discharge takes place. The 
condenser potential drops to about 18 v, after 
which the grid regains control and the con- 
denser starts to charge up again. This occur- 


SECRET 


THE DETONATOR CIRCUIT 


129 


rence is known as “dumping.” In the arc dis- 
charge, the thyratron begins to conduct within 
10 |isec after the signal is impressed on the 
grid. The effective thyratron impedance de- 
creases to about 10 ohms, thus permitting a 
very high peak surge current in the neighbor- 
hood of 6 amp. The discharge is over within 
about 50 psec. When used with rockets which 
suffer badly from afterburning, this phenome- 
non of dumping permits the use of radio prox- 
imity fuzes without undue incidence of early 
functions. At the same time, it permits the fuze 



Figure 51. Distribution of RC arming times in 
terms of the median arming time. 


to function properly within the shortest per- 
missible time after burning has stopped. If 
afterburning is severe, the thyratron may dump 
several times before electric arming occurs. In 
this way, the use of RC arming provides insur- 
ance against premature fuze functions which 
might otherwise occur shortly after mechanical 
arming. 

Arming Pulse Protection. In some of the 
fuzes, such as those designed for use on mortar 
shells, mechanical arming causes a pulse to 
originate in the oscillator. This voltage pulse 
cannot be protected against by means of the 


condenser in the thyratron grid circuit, which 
only decreases the effect of the thyratron plate 
pulse. The use of RC arming does eliminate the 
effect of such arming pulses, but it requires the 
use of a detonator firing condenser in addition 
to the filter condenser. This necessitates the 
allocation of space to two large components 
in the fuzes where the space requirements are 
most critical. As there are no afterburning 
problems with a mortar shell, an electric arm- 
ing system which would eliminate the effect of 
the arming pulse is all that is necessary. Such 
a system has been developed which also permits 
the use of the same condenser for filtering the 
rectifier output and for firing the condenser. 
The scheme consists in having large negative 
voltage on both the thyratron and amplifier 
grids, in addition to the normal grid bias, be- 
fore mechanical arming. This C voltage is large 
enough to bias the amplifier tube beyond cutoff. 
At mechanical arming the additional C bias is 
eliminated, permitting the amplifier to start 
functioning. The time constants in the fuze cir- 
cuits are so adjusted that the arming pulse 
from the oscillator is harmlessly over before 
the amplifier has reached its normal operating 
point and before the thyratron grid bias has 
reached its normal value. 

Other Arming Methods. Several other elec- 
tric arming methods have been used during the 
development period. One method of eliminating 
the pulse which occurs at arming is to use a 
system which does not change the potential at 
any point in the fuze. Two of the systems in- 
volve only the detonator, which must fire in 
order to initiate the explosive in the projectile. 
The first one consisted of having a wire short- 
ing the detonator before arming, so that all 
the circuits would have reached equilibrium by 
the time the detonator was unshorted at arm- 
ing. This method was abandoned because it did 
not assure perfect safety, because of the possi- 
bility of the shorting contact opening prema- 
turely due to vibration or shock. Moreover, 
there was difficulty in keeping the thyratron in 
the nonconducting state at arming if a firing 
signal reached the thyratron grid before arm- 
ing. This method was thus used primarily as a 
safety device rather than as an arming method. 
It was replaced by a system which used a 10- 




130 


ELECTRONIC CONTROL SYSTEMS 


megohm resistor in series with the detonator. 
The resistor was shorted at arming. If the 
thyratron fired before arming, the 10-megohm 
resistor limited the current flowing through 
the detonator to a very small value, on the 
order of 12 qa, so that the heat generated in 
the detonator could be safely dissipated. This 
current is so small that, even if all the heat 
energy produced on the detonator bridge wire 
remained there, it would take several hours to 
initiate the explosion. The factor of safety in- 
volved is enormous. The minimum constant 
current which will fire the detonator is about 
90 ma, 173 and the detonator will function in 
about 5 msec. The heat produced by any small 
current can be safely conducted away 57 through 
the mercury fulminate, which initiates the ex- 
plosion in the detonator. This arrangement is 
much safer because it is possible to place the 
contacts so that accidental operation due to 
vibration or shock is impossible. It also per- 
mitted the inclusion of a self-quenching feature, 
if the thyratron fired before arming, by con- 
necting a condenser between the thyratron plate 
and ground. This system was the precursor of 
RC arming. 

Other arming systems tried also permit the 
thyratron plate to be at its operating potential 
and rely on preventing the thyratron from 
functioning and thus preventing detonation. In 
one of these systems a large negative bias is 
impressed on the thyratron grid, which is re- 
moved at arming. In order to improve this 
method, an RC time delay was added at the 
thyratron grid to prevent functioning immedi- 
ately after arming had occurred. 

Another arming system was used in some of 
the experimental fuzes developed at the Bell 
Telephone Laboratories. 204 The pentode screen 
resistor is connected to B-f- through the thyra- 
tron plate network. Until mechanical arming, 
when the thyratron plate circuit is closed, the 
pentode screen potential is slightly negative, 
because it assumes an equilibrium potential due 
to the electron current in the tube. The gain 
of the amplifier with this screen potential is 
virtually zero and consequently ho signals are 
passed to the thyratron. After mechanical arm- 
ing there is a time delay during which the 
screen by-pass condenser is charged, before the 


amplifier gain reaches its normal value. The 
voltage transients due to the arming process 
are over before the amplifier is operative, so 
that none of the arming transients can cause 
the fuze to function prematurely. Furthermore, 
as the pentode becomes operative, its plate po- 
tential drops from B+ to its normal operating 
potential and transmits a large negative pulse 
of short duration to the thyratron grid. Still 
another method, the principle of which is still 
in use, is to operate the thyratron filament at 
a lower voltage than the other tube filaments, 
thus increasing the time delay before the thyra- 
tron can function beyond that of the rest of the 
fuze. In this way, most pulses are over before 
the thyratron becomes operable. The lower 
thyratron filament voltage is obtained by in- 
creasing the resistor in series with the thyra- 
tron filament. As used on generator-powered 
fuzes, the net effect is that a higher rotational 
speed is required for the thyratron to be able 
to function than for the other tubes. 


3 ‘ 3 ’ 7 Safety Features 

This part of the report deals only with the 
electric safety features, many of which have 
already been discussed in the preceding parts 
of this section dealing with electric arming. 
Actually, the two are very closely related. The 
primary method for assuring that the fuzes 
will be entirely safe in the unarmed position is 
to make certain that no current can flow through 
the detonator heater wire. This may be done 
either by having the detonator open-circuited 
before arming, which is the method used in all 
production fuzes, or by having the detonator 
short-circuited before arming. By relaxing the 
no-current requirement to permit a minute cur- 
rent, the use of the 10-megohm resistor in series 
with the detonator might also be included in 
this classification. 

The other possible electric safety feature is to 
prevent the thyratron from firing prematurely 
and thus prevent detonation. The methods used 
are RC arming in either the plate circuit or 
the grid circuit of the thyratron. An additional 
safety feature common to all generator-powered 
fuzes is that, as long as the generator is not 


SECRET 


POWER SUPPLIES 


131 


turning, there is no electric energy available in 
the fuze. Hence, the detonator cannot fire. Of 
course, this last feature depends on the exist- 
ence of a leakage path across the detonator 
firing condenser, so that the condenser will not 
still be charged from the previous occasion 
when the generator was functioning. 


3 38 Self-Destruction 

Electric self-destruction [SD] was used in 
many of the battery-powered fuzes (T-5) . When 
these fuzes are used as antiaircraft weapons 
over friendly territory, it is necessary to pre- 
vent them from exploding on ground approach 


last factor caused the largest variation in the 
time delay. If the neon gas is relatively un- 
ionized the striking potential may be increased 
as much as 30 per cent above its normal value. 
Methods used for keeping the gas sufficiently 
ionized to minimize variations in striking volt- 
age were to channel light to the neon tube 
through a Lucite window, and thus ionize the 
gas photoelectrically, and to place a little radio- 
active material on the tube envelope. It was 
found that cosmic radiation did not keep the 
gas sufficiently ionized. 


POWER SUPPLIES 8 


DETONATOR 



Figure 52. Self-destruction circuit used in T-5 
fuzes. 


and inflicting casualties. The method used was 
to explode the fuze from 6 to 11 sec after the 
missile was launched, if it had not already 
functioned. This time limit was long enough 
so that, if the projectile were going to function 
on a target in combat, it would already have 
done so. The SD device consisted of an RC time- 
delay circuit (shown in Figure 52) at the thy- 
ratron grid, which was connected to a neon 
tube. The neon tube used was the General Elec- 
tric Company [GE] NE-23, a 1/25-w lamp 
in a T-2 bottle. When the condenser potential 
reached the striking potential of the neon tube, 
the condenser discharged through the neon 
tube, and thus fired the thyratron, which in 
turn set off the detonator. The time delay in 
this circuit is a function of the resistance, the 
capacitance, and the battery voltage, as well as 
of the neon tube striking potential. In fact, this 


Requirements 

The radio-type proximity fuze requires an 
electric power supply which provides filament, 
plate, and grid bias voltages to the electronic 
system and which ultimately delivers a current 
surge to the electric detonator upon actuation 
of the fuze. The power supply has, therefore, 
a position of prime functional importance. The 
quality of overall fuze performance cannot ex- 
ceed that of the power supply. Much effort has 
been directed toward the design of a power 
supply meeting the varied requirements pecul- 
iar to proximity fuze operation. 

Because of the urgency of the program it 
was not practical to follow an optimum pro- 
cedure of setting up rigid functional specifica- 
tions for each part of the device and aiming all 
development to these prescribed requirements. 
Instead all parts of the device were under 
simultaneous development toward rather elastic 
specifications. Progress of one phase invariably 
produced a concomitant change in the mini- 
mum requirements of another phase. 

The initial goal was to realize rapidly a fuze 
design which would provide consistent function 
even if expediency required compromise of the 
ultimate qualities which were visualized for 
the fuzes. Subsequent redesign was relied on 
to introduce improved versatility, performance 

£ This section was written by J. G. Reid, Jr., of the 
Ordnance Development Division of the National Bureau 
of Standards. 


SECRET 


132 


ELECTRONIC CONTROL SYSTEMS 


quality, ruggedness, and simplicity of construc- 
tion. This general philosophy held not only in 
the design of the unit as a whole but also in the 
design of subassemblies, such as the power sup- 
ply. The following general specifications for the 
power supply developed during progress of the 
work. They represent partly initial ideas and 
partly modifications imposed by service con- 
siderations. 

The primary requirement upon the power 
supply system is to furnish adequate operating 
power to the electronic system. No compromise 
can be made on this point. Accordingly, mini- 
mum requirements for A, B, and C supply were 
established on the following bases: 

Filament Supply. Circuit designs utilized 
electron tubes of maximum 1.5-v nominal fila- 
ment operation. Other tube types requiring 
lower filament voltages were adapted to 1.5-v 
supply by use of the proper filament dropping 
resistors. At normal filament voltage various 
tube types drew currents ranging from 70 to 
220 ma. The tube complements of various fuzes 
had filament requirements ranging from 450 to 
750 ma, equivalent to 0.6 to 1.1 w. The fore- 
going are d-c values or rms a-c values. 

Plate Supply. Plate current demands of the 
electronic systems of various fuzes were rela- 
tively uniform. Radio-frequency oscillators 
drew an average of 12 ma at 135 v with a 
spread of about ±2 ma. Amplifiers in all cases 
drew less than 0.5 ma at 135 v. Thus, total plate 
circuit requirements lay between 2 and 3 w 
supplied at 135 to 150 v. 

Bias Supply. Negative grid-bias voltages of 
about 6 v to the thyratron and 1.5 v to the 
amplifier were also required of the power sup- 
ply. These voltages were applied to such high- 
resistance loads that the power involved was 
negligible. 

Detonator Firing. Type BS-4 and BS-5 det- 
onators (see Section 3.3) were used in all fuzes 
developed by Division 4. Actuation of either of 
these required an internal dissipation of 1 mil- 
lijoule of electric energy within the duration 
of 1 msec, or great energy over a longer period. 
A minimum of approximately 5 milli joules was 
required from the power supply within 1 or 
2 msec, the excess supplying energy losses else- 
where in the firing circuit and insuring con- 


sistent function of the detonator. As explained 
in Section 3.3, it was found expedient to draw 
this energy from a noninductive capacitor, 1 mf 
or more in capacitance and charged to the volt- 
age of the plate supply, i.e., at least 100 v. This 
corresponded to a current peak in excess of 
6 amp. The charging of the detonator-firing ca- 
pacitor represented a negligible load on the 
power supply. However in power sources where 
the terminal voltage deteriorated with time the 
lower voltage limit required for the capacitor 
became very important. 

Life. It was required that the power supply 
maintain adequate voltage and power over an 
operating period of at least 1 min. Testing re- 
quirements presented additional demands and 
when the fuze power supply was used for test 
purposes (in production) approximately 10 min 
additional life was essential. 

Indefinite shelf life of the power supply was 
desired but this requirement was waived in 
some of the earlier battery-powered fuzes. 

The power supply was required to operate 
compatibly with the electronic system of the 
fuze, not only in supplying operating voltages 
sufficiently constant and noise free, but also in 
not introducing excessive electric or mechanical 
disturbance by its own operation. 

Stability. Relatively small fluctuation in the 
B supply voltage could cause fuze malfunction. 
If the noise frequency coincided approximately 
with that of amplifier peak gain, 0.03 per cent 
magnitude was sufficient amplitude. Random 
fluctuations of nearly twice this value were 
permissible. Fluctuation in the A supply of 
about the same absolute amplitude (or 100 
times greater in percentage) was tolerable. In 
summary, the voltages supplied had to be es- 
sentially noise free. The precise value of toler- 
able noise depended on the character of the 
noise. This has been discussed in Sections 3.1 
and 3.2. 

It was further necessary that the power 
supply, if it contained any moving parts, intro- 
duce a minimum of mechanical disturbance to 
the electronic system. The maximum tolerable 
amplitude of vibration cannot be specified. It 
depends necessarily on the type of construction 
and the care that has been taken in designing 
both circuits and components. It can be noted 


POWER SUPPLIES 


133 


that the use of high-speed rotating or vibrating 
parts was recognized as a possible source of 
mechanical disturbance and consequent awk- 
ward design problems. 

Ambient Conditions. The range of ambient 
conditions for fuze operation was made pro- 
gressively broader. For the majority of the 
fuzes developed, satisfactory operation was re- 
quired in the temperature range from —40 to 
+60 C, and from 0 to 100 per cent relative 
humidity. This overall requirement was im- 
posed also on the power supply. Further it was 
desirable that proper fuze operation be obtained 
after the unpackaged fuze had been maintained 
under any such conditions for as long as 
24 hours prior to use. 

The fuze, including power supply, was, with 
suitable moistureproof packaging, to have an 
indefinite shelf life under the same ambient 
conditions as for operation. 

Ruggedness. Minimum requirements for the 
mechanical strength and ruggedness of the 
power supply were identical with those for 
the fuze unit as a whole. In use it should per- 
form satisfactorily after setback (for rocket 
application, 250# maximum; for mortar appli- 
cation, 10,000# maximum). No unusual precau- 
tions should be required in fuzing or in the 
handling of fuzed projectiles beyond the care 
exercised in handling ordinary point-detonating 
fuzes. The packaged bulk lots of fuzes should 
be capable of withstanding the rough handling 
such items customarily encountered in field 
storage and delivery. 

Size. With regard to physical design it 
was desirable that the power supply be small 
and of proper shape to match the remaining 
sub-assemblies of the fuze. The particular 
volume corresponding to “small” was progres- 
sively reduced as the program advanced. In 
first designs the power supply was allotted 
about 12 cu in. in the shape of a cylinder 2.5 in. 
outside diameter and 2.4 in. long. In later 
models the total volume was reduced to less 
than half this value. 

It was a prime requisite that the power sup- 
ply be adaptable to quantity production, at least 
with regard to simplicity of construction. Econ- 
omy of material was not a basic consideration 
except in the case of strategic war materials. 


3 ’ 4 ' 2 Survey of Possible Sources of Power 

In the development of a power supply to meet 
the foregoing specifications, serious consider- 
ation was reduced to two general types, those 
using batteries to derive the required electric 
energy from a chemical source and those em- 
ploying electric generators driven by an input 
of mechanical energy. 

The electric demand upon the supply was a 
maximum of 3 w for the plate circuit and 1 w 
for the filaments. With a design excess of 25 per 
cent this indicated 5 w for the power supply 
output. The service life was to be a maximum 
of 60 sec. Thus, for design purposes 300 j was 
taken as the energy requirement upon a power 
supply of battery or of generator type. 

The space available for a battery-type power 
supply was of the order of 10 cu in. or 160 cu 
cm. This permitted a battery mass of about 
250 g. The energy density of ordinary batteries 
ranged from about 10 to 30 whr per kilogram, 
i.e., 40 to 120 j per gram. Thus a minimum 
energy content of 10,000 j could be realized 
from a battery of acceptable dimensions. The 
total service demand of 300 j then represented 
only 3 per cent of the minimum expected total 
energy within a 60-sec period. This was clearly 
a tolerable class of battery service. 

Dry Batteries. The ordinary carbon, zinc, 
ammonium chloride dry battery presented itself 
as the most readily available source of energy. 
It was the consensus, however, that consider- 
ations of delayed service and performance at 
low temperatures would significantly limit its 
usefulness. 2 Although these dry batteries could 
initially fulfill a pressing need with minimum 
delay, it seemed doubtful that they could be 
sufficiently improved as to be rendered com- 
pletely satisfactory. The ultimate solution 
would lie in some basically superior power 
supply system. 

Reserve Batteries. A reserve battery, in which 
the electrolyte was introduced just prior to use, 
could obviously meet the requirements of an 
indefinitely delayed service period. Further- 
more, a battery of this type exhibiting excellent 
low-temperature performance had been devel- 
oped by the Electrochemical Section of the 
National Bureau of Standards. 3 It used lead 


SECRET 


134 


ELECTRONIC CONTROL SYSTEMS 


oxide electrodes and a perchloric acid electro- 
lyte. Some problems persisted, however, with 
regard to the introduction of the electrolyte. 

Two alternatives existed here : electrolyte 
could be carried, separately packaged, within 
the battery assembly to be actively introduced 
upon application of some force due to projectile 
acceleration; or electrolyte could be packaged 
entirely separately from the battery and fuze, 
for introduction shortly before the insertion of 
the fuze into the projectile. The former required 
the development of novel battery designs to 
insure the rapid and proper distribution of 
electrolyte and the maintenance of operating, 
electrically discrete cells. The latter necessi- 
tated the development of special filling equip- 
ment and techniques which would be suitable 
for the uncontrolled conditions of field use. 
Also, the battery once made active could have 
a shelf life of approximately one day. After 
this period it would become useless, since re- 
charging had proved unfeasible. Because of 
these disadvantages most engineering effort on 
electrolyte introduction was directed toward 
setback actuated systems. Although this method 
appeared possible in rocket and mortar appli- 
cations, it was recognized that some externally 
triggered force would have to be provided in 
the case of bomb application where no setback 
would be present upon release. 

The principal difficulties expected in the de- 
sign of a reserve battery supply system lay in 
providing a high-voltage section consisting of 
a multiplicity of series connected cells using 
electrolyte from a common source. Here the 
problems of rapid thorough distribution of 
electrolyte and its subsequent retention with- 
out intermittent short circuiting became acute. 

Battery Vibrator. Consideration was given 
the use of a vibrator high-voltage supply. Here 
a single low-voltage high-capacity battery could 
supply both filaments and the vibrator input. 
The design study of such a system was under- 
taken by the Washington Institute of Tech- 
nology. Although their work indicated the gen- 
eral feasibility of this system, 203 it was not 
carried to the point of achieving a battery, 
vibrator, transformer, rectifier, and filter of 
the requisite small size. 

Generator. The optimum solution of the 


power supply problem appeared to lie in the 
use of a mechanically driven rotary generator. 
Such a system offered several advantages, as 
follows : 

1. An indefinite delay prior to use would not 
adversely affect its performance. 

2. The generator would not be appreciably 
affected by temperature extremes. 

3. The entire fuze unit, including power sup- 
ply, could be shipped into the field assembled 
for use. No final assembly and test just prior 
to use would be required. 

4. The rotating system of the generator could 
be coupled to suitable gearing to provide a me- 
chanical arming and SD feature, if desired. 

5. If the generator were wind-driven by the 
flight of the projectile, a considerable additional 
safety would accrue, since the power supply 
would be inert prior to the period of service. 

Since the generator served merely as a con- 
verter rather than a storage source of energy, 
it could be quite small. A volume of 2 to 3 cu in. 
would suffice for an alternator of requisite 
power. The additionally available space of 8 or 
9 cu in. could accommodate the rectifier-filter 
system and the prime mover for driving the 
generator. 

Prime Movers for Generators. Two basically 
different conceptions of the prime mover were 
apparent: (1) a storage system which received 
an initial charge of mechanical energy prior 
to the service period, and (2) a wind-driven 
system continuously drawing energy from the 
windstream during the flight of the projectile. 
A rotating flywheel, a stressed spring, or a vol- 
ume of compressed gas represent mechanical 
systems of the storage type. In any case a 
mechanical input of approximately twice the 
electrical requirements would be necessary, 
since efficiency of little more than 50 per cent 
could be expected from a miniature generator. 

1. Storage systems. The necessary 600 j of 
mechanical energy can be stored in a flywheel 
of reasonable dimensions and at reasonable ro- 
tational speed. The basic expression for the 
energy of rotation, W = Vvlw 2 , becomes in the 
case of a simple cylinder of radius r, axial 
length l, density p, and rotational frequency f, 
about the axis 

W = tt 3 r 4 l P f 2 . 


POWER SUPPLIES 


135 


Thus the rotation of a steel cylinder, 1 % in. in 
radius and 1 in. in axial length, represents 
2,600 joules at 40,000 rpm and 2,000 joules at 
35,000 rpm. The required energy could be taken 
within this frequency range and a reserve con- 
tent of 200 per cent would remain at frequen- 
cies above 20,000 rpm. The mass of this rotor 
is about 1.5 lb. The questions of adequate dy- 
namic balancing and the design of bearings for 
the system arise as problems in development 
engineering, possibly difficult but certainly not 
insoluble. 

The directly coupled flywheel-alternator sys- 
tem would have the advantage of permitting a 
completely sealed assembly. The fuze could 
carry external electric contacts by which high- 
frequency alternating current could be applied 
to the alternator for running it synchronously 
to charge the rotor to the proper frequency of 
rotation. 

The system could be regarded as an a-c stor- 
age battery which delivers alternating current 
over the frequency range through which it has 
just been charged. It has the inherent disad- 
vantage of requiring an electric charging 
source of adjustable frequency and reasonably 
high-power output, which must be available 
immediately before the launching of the fuzed 
missile. If the charging system fails, the fuze 
cannot be put into operation. 

The operational disadvantages of field “charg- 
ing” of rotors and the attendant equipment, 
coupled with the possibilities of engineering 
difficulties in massive fast-rotating systems pre- 
cluded the serious pursuit of this method for 
driving generators. It nevertheless appears 
feasible, especially where the complete sealing 
of a generator powered fuze is required. 

Energy content calculations indicate that a 
wound spring of adequate capacity would be 
prohibitively large. The energy content of a 
coiled clock spring is given approximately by 

w BTLS 2 
TF = -QE~> 

where B is the breadth, T the thickness, L the 
length of the spring, S the applied stress, and 
E Young’s modulus for the material. 

Since BTL represents the solid volume of 


spring material, the energy density of spring 
material is given by 

W 

V 6 K 

In the case of spring steel stressed nearly to 
the elastic limit (S = 2 X 10 5 psi and E — 3 X 
10 7 psi) 

W 

y = 25 joules /in. 3 (approximately). 

Assuming a 50 per cent efficiency of space uti- 
lization for the spring system, 48 cu in. are re- 
quired for an energy content of 600 joules. This 
value is an order of magnitude too great for 
warranting its consideration as an energy 
source for the fuze power supply. 

The use of a compressed volume of air for 
energy storage appears theoretically possible 
but requires extremely high pressures for hold- 
ing the reservoir dimensions within permis- 
sible limits. Even assuming that the release is 
slow enough to approach isothermal conditions, 
a reservoir of 3 cu in. capacity would have to 
contain air initially at 100 atm to drive a 67 per 
cent efficient turbine for an adequate energy 
delivery coincident with a pressure drop to 16 
per cent of the initial value, and this would 
correspond to an energy reserve of only about 
80 per cent. Furthermore, this system of 
energy storage would introduce considerable 
engineering difficulty in the design of the high- 
pressure air flask, reduction valve and turbine 
system. It was not given consideration in the 
power supply development. 

Another somewhat different storage method 
has been proposed by various participants in 
the program. This involves conversion of chem- 
ical energy to mechanical energy. A slow-burn- 
ing powder might be used to provide the driv- 
ing power for a generator. Detailed considera- 
tion of the method has not been made. 

2. Wind-driven systems. For driving a 
power supply generator it appeared most ad- 
vantageous to use a vane or turbine driven by 
the wind stream of the missile in flight. This 
side-steps the requirement of storing within 
the fuze sufficient energy for operation during 
its entire service period, but instead imposes 
the demand that the wind drive supply adequate 


SECRET 


136 


ELECTRONIC CONTROL SYSTEMS 


mechanical power to the generator at all times 
during its service period. Thus, the spread in 
air travel characteristics of various projectiles 
under various applications becomes a compli- 
cating factor. 

A projectile moving with air velocity v and 
carrying a vane or turbine of efficiency e devel- 
ops power in the turbine shaft with an attend- 
ant incremental force of drag f (1 on the pro- 
jectile. 

Thus, 

P = ef d v. 

The deceleration a upon the projectile of mass 
m is 

a = U = P_ 

m emv 

For design purposes, P has a value of 10 w, so 
that an electric output of 5 w is available from 
a 50 per cent efficient alternator. The aerody- 
namic efficiency e of the vane or turbine will 
vary with airspeed and with load, but for all the 
situations of service to be met by the fuze it 
should exceed 50 per cent. Using these bases, 
the drag effect of the vane can be approximated 
for various projectiles of minimum sizes and at 
minimum airspeeds as follows. 



Mass, 

Airspeed 
approximated 
minimum 
during serv- 

Deceleration 
due to drag 


loaded 

ice period 

of vane or 

Projectile I 

(approx.) 

of fuze 

turbine 

Mortar shell 

M-43, no incre- 
ment of charge 

7 lb 

150 fps 

0.14 g 

Bomb M-30, re- 
lease at 150 
mph 2,500 ft air 
travel 

100 lb 

350 fps 

0.004.a 

Rocket T-22, at 
extreme range 

40 lb 

500 fps 

0.007# 


The incremental drag due to a power supply 
vane system is obviously of no importance when 
compared to other sources of drag in bomb and 
rocket applications. In the case of the lightest 
mortar shells, it is evident that the drag may 
be great enough to cause a measurable shorten- 
ing of range. However, even here the effect 
does not appear sufficiently serious to outweigh 
the operational and constructional advantages 
which the wind-driven system affords. 


The system requires the design development 
of vanes or turbines suitable for use with the 
various bombs, rockets, and mortar shells. 
Other design problems on high-speed bearings, 
coupling elements, vibration isolation, etc., are 
inherent to the rotary alternator rather than 
the wind drive. 

Selected Methods. Three methods of obtain- 
ing electric power for the fuzes were selected 
for intensive investigation. These were 

1. Dry battery, 

2. Reserve battery, 

3. Wind-driven generators. 

The first of these was selected for reasons of 
expedience and was used in the T-5 and T-6 
fuzes. The third method was used in all later 
fuzes. The second method was pursued until it 
was demonstrated that wind-driven generators 
were practicable, at which time further work on 
reserve batteries was discontinued. Summaries 
of the work on these methods are given in the 
next three sections. 


Dry Batteries 

Dry batteries were selected for use in power 
supplies for early experimental fuzes and for 
production fuzes T-5 and T-6. They were se- 
lected because they were immediately available 
in quantity. Their limitations at low tempera- 
ture or in delayed service were recognized. 

Development work on dry batteries fell into 
two major categories: (1) the assembly and 
packaging of the best available cells into a me- 
chanically suitable power supply unit, and (2) 
an electrochemical study of the individual cells 
with the aim of improving their character- 
istics. 

The first battery packs were improvised as- 
semblies of commercial miniature dry cells. 
These were to meet the urgent need of power 
units to permit proof testing of early experi- 
mental electronic assemblies of the fuze. Their 
design and operating characteristics were con- 
ventional and warrant ho particular comment. 

BA-55. One basic production dry battery 
pack was developed. This was made in two 
models: the BA-55, for powering rocket fuzes 
T-5 in plane-to-plane use, and the BA-75 for 


SECRE 


POWER SUPPLIES 


137 


T-6 fuzes in ground-to-ground use. The two 
models were identical mechanically and in bat- 
tery make-up but differed in their electric arm- 
ing and SD circuits, as shown in Figure 53. 
The electric arming and SD characteristics 
have been discussed in Section 3.3. 

The BA-75 unit is shown in Figure 54. The 
plastic container is 2.60 in. in diameter and 


TOP TERMINALS 




Figure 53. Schematic circuit diagrams for pro- 
duction battery packs. Top, BA-55 used in origi- 
nal T-5 fuze for plane-to-plane application. (Cf. 
Figure 12, Chapter 4.) Bottom, BA-75 used in 
T-6 fuze for ground-to-ground application, and 
with special switch in later T-5 fuze for plane- 
to-plane application. 


2.31 in. in height. The pin sockets on the ends 
of the container provide contact with the elec- 
tronic assembly and with the arming switch- 
detonator assembly. The weight of the battery 
is about 10 oz. 

Individual cells of the battery pack were all 
of the zinc, carbon, ammonium chloride type 
with manganese dioxide depolarizer. The, fila- 
ment supply consisted of a parallel pair of zinc 


cup cells, of miniature (No. AA) dimensions. 
The plate and C-bias battery consisted of four 
series stacks of cake-type cells (National Car- 
bon layer-built). The individual cakes were of 
rectangular cross section, 0.75 in. by 0.5 in., 
with rounded corners and were a little under 
0.2 in. in thickness. The four stacks, totaling 
96 cells, were arranged with the two cylindri- 
cal A cells in a circular array around a cylin- 
drical noninductively wound paper capacitor of 
1.5 mf capacity. The capacitor served as a res- 
ervoir for the detonator firing charge. 



Figure 54. Battery pack, BA-75. At left is 
complete unit. At right is similar unit with end 
plate removed. Six stacks of layer built cells for 
B and C voltage, two cylindrical A cells, and 
detonator firing capacitor can be seen. 


The electric characteristics of the BA-55 
were as follows. 

A voltage 1.50 min, open circuit, 20 C, new battery. 

1.20 min, 3.3-ohm load for 30 sec, new 
battery. 

B voltage 138 min, open circuit, 20 C, new battery. 

120 min, 8,800-ohm load for 30 sec, new 
battery. 

C voltage 6 min, open circuit, 20 C, new battery. 

Less than 2 per cent decrease from open- 
circuit voltage, 4-megohm load for 14 
days, 20 C, new battery. 

Temperature and Storage Properties . The 
BA-55 could operate at —15 C with less than 
10 per cent decrease in these voltages, and after 
three months storage at 20 C could operate at 
20 C or at —15 C within 10 per cent of its cor- 
responding voltage output when new. The fol- 
lowing table summarizes the performance of 
a typical BA-55. 


SECRET 


138 


ELECTRONIC CONTROL SYSTEMS 


Delayed service performance of dry batteries 
is much improved if the storage is at low tem- 
perature. Three years’ storage at 9 C, two 
years, at 20 C, or six months’ at 40 C causes 
about the same deterioration in dry batteries. 
In military field storage it could be expected 


Test 


Initial load 

Final load 

temp. 

Open-circuit 

voltage 

voltage 

(C) 

voltage 

(3.3-ohm load) 

(30 sec) 


New battery 


—15 

(B) 134 

120 

110 


(A) 1.54 

1.30 

1.20 

20 

(B) 140 

132 

128 


(A) 1.57 

1.42 

1.39 


Three months’ storage at 20 C 



(8,800-ohm load) 


—15 

(B) 133 

118 

108 


(A) 1.51 

1.29 

1.20 

20 

(B) 138 

128 

124 


(A) 1.56 

1.40 

1.37 


that at best temperatures of 20 to 25 C would 
be maintained. Thus protection against battery 
deterioration could best be provided by check 
on batteries immediately prior to use in the 
field. 

In this connection the flash current delivered 
by the battery through a low (0.01 ohm) re- 
sistance deadbeat ammeter was used. The 
BA-55 at 20 C after three months’ storage at 
20 C would give a flash current of 8 amp for 
the A and 0.75 amp for the B section. 

Fully adequate low-temperature service was 
inherently impossible with the ammonium 
chloride cells of the BA-55. Although the service 
was marginally acceptable at —15 C, it became 
completely impossible at about —25 C where 
the electrolyte froze. 

Consideration of methods for keeping the 
ammonium chloride cells warm during service 
indicated no practical solution. Preheating was 
inconvenient and uncertain. The use of ther- 
mal insulation increased bulk where it could 
not be tolerated. Although it was found pos- 
sible to heat the battery electrically by passing 
an alternating current through it up to the 
start of the service period, this was inconven- 
ient and hazardous when applied to live fuzes. 

Improved Dry Batteries. A dry battery 
power pack with satisfactory low-temperature 
characteristics appeared practical only with a 
basic cell which was superior to the zinc, car- 


bon, ammonium chloride cell used in the BA-55. 
A study of electrolytes and electrodes was un- 
dertaken by the National Carbon Company. 199 

For low-temperature performance, calcium 
chloride was found the best of the several elec- 
trolytes. Acetylene black was found superior to 
conventional carbons for the positive electrode. 
Synthetic manganese dioxide was found su- 
perior to refined natural ore (Brazil earth) for 
the depolarizer. It was also established that 
several small and apparently insignificant as- 
sembly details required careful control for in- 
suring quality performance at low tempera- 
tures. 

When calcium chloride cells embodying these 
improvements were tested at —40 C, after 6 
months’ storage at 20 C, it was found that the 
A voltage fell to 1.1 v in delivering 170 ma for 
15 sec, and that the B voltage fell to about 
1.14 v per cell in delivering 1.25 ma for 15 sec. 
Both of these values were far short of the mini- 
mum requirements from the power supply and 
it was decided that the prospects of developing 
a satisfactory dry cell did not warrant further 
investigation. 

3,4,4 Reserve Batteries 199 

As has been stated in Section 3.4.2, the per- 
chloric acid cell had satisfactory service char- 
acteristics in all respects (including low-tem- 
perature properties) except for an extremely 
short delayed service period. The following 
table compares the perchloric acid cell, 3 the 
common dry cell, and the common lead cell in 
a few pertinent criteria. 



Perchloric 

Cell 

Dry Cell 

Lead Cell 

Open-circuit 

voltage 

1. 8-2.2* 

1.5-1. 6 

2.12 

Output, amp- 

hr/kg 

22 

10 

9 

Output, whr/kg 

39 

12 

17 

Freezing point, 

degrees C 

— 60f 

—25 

—65 

Flash current 

(miniature 

1.2 amp 

0.01 amp 

0.37 amp 

cells) 

at — 50C 

at — 30C 

at — 40C 

Internal resist- 

ance (minia- 

1.0 ohm 

150 ohms 

5.6 ohms 

ture cells) 

at — 50C 

at— 30C 

at — 40C 


* Depends on acid concentration. 

t Minimum freezing point concentration gives — 59 C, but this is 
lowered by the solution of lead perchlorate into the electrolyte. 


SECRE' 


POWER SUPPLIES 


139 


The perchloric acid cell uses lead-lead oxide 
electrodes and sustains the following reaction 
during discharge: 

Pb 0 2 + 4HC10 4 + Pb 

-H>Pb(C10 4 ) 2 + 2H 2 0 + Pb(C10 4 ) 2 . 
The perchloric acid cell differs significantly 
from the sulphuric acid-lead cell in that the lead 
perchlorate evolved on discharge is soluble in 
the perchloric acid electrolyte and does not 
plate out on the electrodes. 

Developmental work on the perchloric acid 
cell was concentrated on the design of a reserve- 
type battery having the same outside dimen- 
sions as the BA-55. It was recognized that such 
a unit would not be usable with bomb fuzes, 



Figure 55. Reserve battery pack, first experi- 
mental design. This unit contained B cells only. 
Section of unit is at left. Glass ampule contain- 
ing electrolyte occupied central space. Cell as- 
sembly, without hairpin plates, is at right. 
(Photograph by National Carbon Company.) 

since it required setback forces for distributing 
electrolyte. However this appeared to be the 
only practical means of introducing electrolyte 
just prior to the service period, as necessitated 
by the short permissible service delay with 
perchloric acid cells. 

The first experimental design of a reserve 
cell, built to the same dimensions as BA-55, is 
illustrated in Figure 55. This used cylindrical 
plastic tubes molded in concentric circles for 
housing the B cells. Nickel hairpin jumpers, 
having one end plated with lead, the other 
plated with lead oxide, formed the series of 
electrodes. Asbestos separators were mounted 


between electrodes in each cell. The acid was 
contained in a centrally placed glass ampule. 
This broke on setback and flooded the open ends 
of the cells. Subsequent ballistic forces being 



Figure 56. Reserve battery subassemblies. Top, 
radial plate B cell; bottom, ampule cavity and 
electrolyte distributor which was used in one 
experimental model. A cell was located at the 
bottom of ampule cavity. (Photograph by Na- 
tional Carbon Company.) 

oppositely directed to those of setback drove 
the acid into the individual cells. 

In proof tests of these batteries many volt- 
age transients were present because of im- 
proper filling of the cells. 

To improve this condition the radical revi- 
sion shown in Figure 56 was tried. Here the B 
and C cells are formed by the many rectangu- 
lar nickel plates which were molded into the 
plastic base, radially arrayed about the walls of 
a central plastic cup. As before, filling occurred 
upon ampule breakage. The acid passed through 
a fine wire mesh which removed broken glass 
into the flat cup A cell and overflowed the cup 
walls to fill the peripheral B and C cells. Re- 
tainers in the form of perforated Vinylite 
Krene, 0.008 in. thick, were used in each cell. It 
is notable that the nickel cell walls were plated 




secr: 


140 


ELECTRONIC CONTROL SYSTEMS 


after being molded into the plastic base. With 
the cells filled with a solution of HC10 4 and 
PbO in water, a current of 10 ma for 8 min 
plated an adequate layer of Pb on one face 
and Pb0 2 on the other. The nickel wall thus 
connects the B and C cells in series. 

This model showed some improvement, but 
in field tests, used with fuzes on rockets, there 
were still an excessive number of malfunctions. 
These were undoubtedly due to voltage tran- 
sients in the B supply. Although methods were 
proposed to improve the battery further, de- 
velopment was discontinued because the wind- 
driven generator (see Section 3.4.5) had been 
proved-in as a generally satisfactory source of 
electric power for fuzes. 


Wind-Driven Generators 

General. The wind-driven power supply con- 
sisted of three principal elements. 

1. The driver (windmill or turbine) . h 

2. The generator. 

3. The rectifier and filter. 

These operated so interdependently, electrically 
and mechanically, that their design was neces- 
sarily evolved in close coordination. 

The basic mechanical design of the entire 
power supply hinged upon a choice of method 
for transferring energy from the airstream 
around the missile to the rotor of a generator 
which was preferably located in the rear of the 
electronic assemblies of the fuze. One method 
was to mount a driver vane on the nose of the 
fuze and couple this to the generator by means 
of a central drive shaft extending through the 
electronic assemblies. A second method was to 
admit air through intake ports or scoops in the 

h The driver for the generator on most generator- 
powered fuzes was a windmill mounted externally on the 
front end of the fuze. Generators on other fuzes were 
driven by turbines located in air ducts farther back in 
the fuze. The windmills were commonly called propellers 
because of their appearance. Most of the reference re- 
ports used the term propeller exclusively. The windmills 
were also extensively referred to as vanes, a term intro- 
duced by the Army. Both the terms, propeller and vane, 
were used to specify externally mounted drivers. In- 
ternally mounted drivers were referred to as “turbines.” 
Occasionally the term impeller has been used (although 
probably incorrectly) to include both types of drivers, 
i.e., windmill and turbine. 


airstream, pass it through a duct to a turbo- 
generator assembly and thence to exhaust 
ports. 

The first method received emphasis since the 
nose-mounted vane permitted the development 
of a generator-powered fuze embodying much 
of the basic design of the battery-powered T-5 
fuze. Electronic assemblies could be revised to 
give clearance for a central drive shaft of small 
diameter. The inclusion of an air duct of ade- 
quate cross section would have required drastic 
revision. Additionally an awkward problem 
arose in exhausting air from a fuze mounted in 
the closed encasing can proposed for use. On 
the basis of a nose-mounted vane, the following 
fuzes were developed for use on bombs and 
rockets: T-50-E1, T-50-E4, T-89, T-90, T-91, 
T-92, T-51, T-30, and T-2004. Figure 57 shows 
a sectional T-51 fuze as typical of the mechani- 
cal design of fuzes of this class. The vane, bear- 
ings, central coupling shaft, and metal encased 
generator can be seen. 


Figure 57. Fuze T-51 with section cut away. 
Nose-mounted vane and central drive shaft to 
generator rotor can be seen. 

This discussion primarily covers the power 
supply of nose-mounted vane fuzes, since these 
were the ones produced in greatest quantity. 
However, other types using turbine drive are 
discussed in less detail. 




POWER SUPPLIES 


141 


Bomb fuze T-82 was developed as a complete 
departure from the nose-mounted vane. This 
used a central air duct from the nose to a turbo- 
generator at the base of the fuze. Peripheral 
exhaust ports were located in the plane of the 
turbine. No encasing can was required. Figure 
58 shows a T-82 fuze sectioned to expose the 
air duct and turbine. A similar basic design 
was used in the miniature mortar fuze T-172. 
Peripheral air scoop, air duct, and exhaust 
ports were used in conjunction with a turbo- 
generator in bomb fuze P-4. (See Figure 48 of 
Chapter 4.) 

Miniature mortar fuzes T-132 and T-171 and 
miniature rocket fuze T-2005 avoided both the 
central drive shaft and the air duct by locating 
a turbogenerator at the nose of the fuze. This 



Figure 58. Fuze T-82 with section cut away. 
Central air duct to turbine can be seen. Gen- 
erator was immediately below and directly 
coupled to turbine. 

was made possible by improvements in methods 
of balancing the turborotor with consequently 
quieter operation and by a redesign of the fuze 
antenna system. A sectioned T-132 is shown in 
Figure 42 of Chapter 4. Intake ports were holes 
punched in the face of the nose cap. Exhaust 
ports were in the side walls of the nose cap. 

A design parameter of common importance 
to all elements of the power supply was the fre- 
quency range in which the rotor system was to 


operate. Low rotational speeds relieved bearing 
requirements, produced lessened centrifugal ef- 
fects and vibration amplitudes, and were gen- 
erally favorable mechanically. High rotational 
speeds increased the electric output from a 
simple generator and also simplified filtering 
because of the higher electric frequency. 

However, the dominant factor in selection of 
the range of operating rotational frequencies 
was that the speed range be removed as far as 
possible from the frequency band to which the 
fuze amplifier responded. Within this band the 
amplifier was highly susceptible to electric 
noise, whether due to generator hum or to volt- 
age induced by mechanical vibration. Ampli- 
fiers for various fuzes were peaked in the ap- 
proximate range of 25 to 200 c, excepting the 
broad-band amplifiers of transverse antenna 
bomb fuzes, which had high gain up to 300 c 
(cf. Section 3.2). Since operation of the power 
supply was not feasible at rotational frequen- 
cies below 25 c, the design was planned with 
operation above 250 c (15,000 rpm) for longi- 
tudinally excited fuzes and above 333 c (20,000 
rpm) for the bar-type bomb fuzes. 

Constancy to about ±5 per cent was required 
in the voltages from the power supply during a 
service period in which the airspeeds encoun- 
tered by the vanes varied by as much as 3 to 1. 
The requisite voltage regulation was provided 
electrically by the addition of a mesh of proper 
impedance to the output circuit of an a-c gen- 
erator. This obviated the requirement of incor- 
porating aerodynamic or mechanical devices in 
the vane or turbine for regulating its rotational 
speed within close limits over a wide range of 
airspeeds. For all except the miniature fuzes it 
was sufficient that operation stay below an 
upper limit of about 40,000 rpm. 

Vane and Turbine Requirements. With re- 
gard to the actual supply of power it was re- 
quired that a vane or turbine under its operat- 
ing load should maintain rotational speed with- 
in permissible limits for all airspeeds encoun- 
tered between the times of arming and of fuze 
function. In most cases permissible rotational 
speeds ranged from 15,000 to 40,000 rpm for 
bomb and rocket fuzes, corresponding to air- 
speeds of 450 to 1,000 fps for bombs and 1,400 
to 800 fps for rockets. Mortar fuzes permitted 


SECRET 



142 


ELECTRONIC CONTROL SYSTEMS 


higher peak values of rotational speed because 
of more compact and better balanced rotor 
assemblies. 

However, the vane or turbine was also to 
serve as an integrator of air travel and a driver 
for the arming system of the fuze. This placed 
the additional requirement that vanes or tur- 
bines of a given type be extremely uniform in 
their rotational characteristics particularly 
over the range of airspeeds met during the 
arming period. This meant uniformity over the 
entire speed range since bombs armed at rela- 
tively low airspeeds, other missiles at higher 
airspeeds. Vanes or turbines for bomb fuzes 
carried the additional requirement that they 
develop sufficient torque to overcome the static 
load of the rotating system at an airspeed of 
300 fps, minimum release speed, and yet de- 
velop less than this static torque at an airspeed 
of 200 fps which might be encountered in an 
open bomb bay. 

The torques required from the vanes and tur- 
bines were small. The static torques of the ro- 
tating systems of the various fuzes in no case 
exceeded 3 in.-oz and averaged about 1.5 in.- 
oz. 151 Running torques were about this latter 
value. 48 At the minimum operating speed of 
15,000 rpm this was equivalent to a mechanical 
input of 16 w, a figure consistent with the elec- 
tric demand of about 7 w at an expected effi- 
ciency of 50 per cent, including frictional and 
other losses. 

Vanes and turbines having the required op- 
erating characteristics were developed for 
quantity production as follows : vanes for bomb 
and rocket fuzes, moldings of phenolic plastic; 
vanes for bomb and rocket fuzes, punchings of 
sheet steel and Duralumin; turbines for bomb 
fuzes, aluminum castings and sheet steel punch- 
ings ; turbines for mortar fuzes, aluminum 
alloy castings. 

Vane and Turbine Design. Representative 
plastic vanes mounted on T-50 and T-51 fuzes 
are shown in Figure 59. These had three 
equally spaced blades with an effective diame- 
ter of 2.5 in. The blade surfaces were helicoids 
so that the vanes could be removed from a one- 
piece mold with a screw motion. Vanes having 
6, 9, and 12 in. of lead (i.e., helical advance in 
one revolution) were used to provide the re- 


quired assortment of rotational speed charac- 
teristics. These are shown in the curves of Fig- 
ure 60 which also includes the characteristics 
of a typical metal vane. 



Figure 59. Plastic vanes on bomb fuzes. Left, 
T-50-E1 ; right, T-51. 


The metal vane is shown in Figures 19 and 
20 of Chapter 4. These were 2 in. in diameter 
and carried 10 blades bent to angles of 55 or 



Figure 60. Rotational speed versus air speed 
for various vanes on T-50 fuze. A, plastic vane, 
6-in. lead; B, Duralumin vane, 2-in. OD, 10 
blades, 55-degree lead angle ; C, plastic vane, 9-in. 
lead; D, plastic vane, 12-in. lead; A, C, D from 
field test data of reference 27; B from field test 
data of reference 28. All tests on M-81A bombs. 

65 degrees relative to their original plane. The 
55-degree metal vane was slightly faster than 
the plastic of 9-in. lead. The 65-degree metal 
was about equivalent to the plastic of 12-in. 
lead. Steel or Duralumin were used for the 


SECRET 


POWER SUPPLIES 


143 


metal vanes. Brass was satisfactory in opera- 
tion but was too susceptible to deformation in 
handling. In some metal vanes, short radial 
ribs embossed along the center line of each 
blade at its narrowest section were found to 
increase the rigidity and eliminate the tendency 
toward blade flutter. (See Figure 19 of Chap- 
ter 4.) 

Both plastic and metal vanes were used on 
bomb fuzes. A tabulation in detail is given in 
Section 5.5 on fuze data sheets. The operation 
of the vanes was affected by the airflow proper- 
ties of the bomb with which they were used. 
They ran slower on larger bombs. The slowing 
was approximately over a 10 per cent range for 
the 100- to 500-lb bombs, another 10 per cent 
for the 1,000-lb and still another 10 per cent 
for the 2,000-lb bomb. This effect was of limited 
consequence for the ring-type fuzes which 
were designed for use on particular bombs. 

However, bar-type fuze T-51 was designed 
for universal bomb service and used a broad- 
band amplifier permitting 20,000-rpm mini- 
mum vane speed during service. Here a plastic 
vane of 6-in. lead was used. Operating speeds 
for this are shown in Figure 61. The bomb is 



VELOCITY (FT/SEC) 


Figure 61. Rotational speed versus air speed 
for plastic vanes on T-51 fuze. A, 6-in. lead, 
M-81A bomb; B, 9-in. lead, M-57 bomb. A from 
field test data of reference 35. B from field test 
data of reference 30. 

the M-81A, 260-lb fragmentation type. The 
curve for a 9-in. lead vane, also open-mounted 
on T-51, is shown for comparison. The extreme 


speeds of rotation for high-altitude release were 
a necessary concession to the attainment of 
high rotational speed at arming for low-alti- 
tude releases, particularly on larger bombs. 



Figure 62. Rotational speed versus air speed 
for metal vanes on T-30 fuze. A, steel vane, 2-in. 
OD, 10 blades, lead angle 55 degrees; B, steel 
vane, 2-in. OD, 10 blades, 65-degree lead angle. 

A from field test data of reference 31. B from 
field test data of reference 32. 

Metal vanes were used on rocket fuzes T-30 
and T-2004. The 55-degree blade angle proved 
suitable for the range of airspeeds encountered. 
A typical speed characteristic of the 55-degree 
metal vane is shown in Figure 62. The charac- 
teristic of a 65-degree blade is included for 
comparison. 

The T-82 turbine is shown in Figure 63. The 
die-cast aluminum base is 2 in. square and 
carries four fixed blades and four alternately 
placed lugs to which were affixed blades of 
steel clock-spring ribbon. In experimental de- 
velopment light springs were used to provide 
a regulating effect. At increased rotational 
speeds the blades were deflected toward a radial 
position both by centrifugal force and by the 
increased air impact. This reduced their effi- 


SECRET 



144 


ELECTRONIC CONTROL SYSTEMS 


ciency as driving blades and also caused them 
to throttle the flow from the adjacent fixed 
blade. However, in the production of T-82, pos- 
sible regulation features were passed over in 
favor of the assurance of greater operating 
uniformity attainable with heavy springs. 



Figure 63. Turbine mounted on base assembly 
of bomb fuze, T-82. 


Nevertheless, as is shown in Chapter 5, uni- 
formity of speeds for the T-82 turbine was 
appreciably less than for other fuzes. A typical 
speed characteristic of the T-82 turbine is 
shown in Figure 64. 

The turbine for mortar fuze T-132 was an 
aluminum casting in the form of a circular base 
1% in. in diameter, carrying eight blades 
shaped as radial spirals. The speed character- 
istic of the turbine for selected extremes of fir- 
ing parameters is shown in Figure 65. The 
curves show rotational speed against time of 
flight. Extremes of airspeed are approximately 
2,000 and 200 fps. 

Bearings. Bearings for the rotating system 
were called on for high-quality performance 
under severe operating conditions even though 
for a very short overall period. They were to 
support the vane or turbine and generator 
rotor at speeds to 40,000 rpm or faster. They 
were to take axial thrusts of as much as 15 lb 
from the airstream and radial thrusts of as 


much as 3 lb per 0.001 in.-oz of unbalance in the 
rotor at top speed. They were to introduce a 
minimum of vibration and electric noise into 
the electronic system. 

Fuzes in final production used commercial 
miniature precision ball bearing assemblies or 
cushion-mounted Oilite bronze sleeve bearings 
in conjunction with accurately balanced rotary 
elements. Although the desirability of such 
bearing systems had been apparent since early 
in the program, precision ball bearings had not 
been immediately available in the necessary 
quantity nor had equipment suitable for rapid 
production balancing operations. Pending pro- 
curement of the former and development of the 
latter, fuzes of the T-50 and T-51 design were 
put into production, using improvised ball bear- 
ings and Oilite sleeve bearings. The success 
attained with these fuzes was due to the careful 
attention in production to dimensional toler- 
ances on components and subassemblies of the 



Figure 64. Rotational speed versus air speed 
for turbine of bomb fuze, T-82. Data from field 
test of reference 42. 

mechanical system. This is discussed in Sec- 
tions 6.4 and 6.5. 

Fuzes using the nose-mounted vane required 
separate bearings for the vane and the genera- 
tor rotor because of the 3-in. separation of 
these elements and because of the assembly 
problem involved. The vane bearing took the 


SECRET 


POWER SUPPLIES 


145 


thrust of the airstream and was necessarily a 
ball bearing. This was located in a strong r-f 
field from the oscillator and consequently was 
seated in a cylindrical brass or steel sleeve 
which extended downward to shield all moving 
parts of the bearing and the upper end of the 
coupling shaft. Vane bearing assembly may be 
seen in Figure 57. (Cf. Figure 18 of Chapter 4.) 

The generator shaft took no axial load. In 
early production the bearings which supported 
it were Oilite bronze sleeves. Final production 
replaced these with precision ball bearings for 
reducing end play and mutation. A ball bearing 
generator is shown in Figure 70 of this chapter 
and Figure 27 of Chapter 6. 



Figure 65. Rotational speed versus time of 
flight for turbine of mortar fuze, T-132. Curves 
are for M-43C mortar shell fired at quadrant 
elevations and with propellant charges as indi- 
cated. 

The coupling shaft between the vane and 
generator transmitted a normal starting and 
running torque of no more than 2 in.-oz. When 
the fuze vane was freed from the block of an 
arming delay mechanism after high airspeed 
had been reached, the starting torque could ap- 
proach 2 in. -lb. A metal shaft could not be used 
because of the noise and loss it introduced in 
passing through the r-f field of the oscillator. 
The required strength in the permissible small 
diameter was obtained by the use of rag-filled 
phenolic resin and other plastics. Even with a 
plastic shaft it was found necessary in the T-51 
to electroplate a floating shield of copper inside 
the %-in. sleeve surrounding the shaft to re- 
duce the loss modulation which was introduced 
at rotational frequency. 

In some vane bearing designs two ball-bear- 


ing assemblies were used. In this case both vane 
and generator rotor spun on established axes. 
The coupling shaft between their respective 
shaft ends was indexed on center pins which 
were fitted loosely enough to allow for the 
maximum tolerable misalignment. In other 
vane bearings a single ball-bearing assembly 
was used. This was mounted on a coupling shaft 
carrying the vane at its upper end and free 
at its lower end. The axis of the coupling shaft 
and vane was established when the free end 
was connected to the generator shaft. 

Fuzes employing turbogenerators required 
only two bearings and no separate coupling 
shafts. Ball-bearing assemblies were used suc- 
cessfully with rotors which were not processed 
for balancing. Sleeve bearings and a single-ball 
thrust bearing were used with the precision- 
balanced turborotor of mortar fuze T-132. This 
is treated in detail in Chapter 4, which also in- 
cludes a discussion of balancing methods and 
equipment. 

Dynamic Balancing. In fuzes having a nose- 
mounted vane, unbalance in the vane was found 
most serious in producing vibration and electric 
noise. This was due to the location of the vane 
farthest from the supporting base, and the 
overhung mounting of the vane relative to its 
bearings. The generator rotors were of about 
the same weight as the vane (1 oz) but pro- 
duced less noise because of their position near 
the base of the fuze and their mounting be- 
tween two bearings. Satisfactory operation of 
a vane, either metal or plastic, was attained if 
its unbalance after mounting were made less 
than 0.001 in.-oz relative to its axis. The bal- 
ancing of individual generator rotors was not 
found to be necessary, provided careful control 
of their dimensions were maintained. 

Electric Design of Generator. Production 
model generators were alternators with sta- 
tionary armature windings and rotary fields. 
Separate windings were used for supplying 
plate and filament voltages. Rotors were small 
disks of Alnico II or IV, magnetized with six 
peripheral poles alternately of reversed polar- 
ity. 

The choice of this design rested on the fol- 
lowing advantages: 

1. It met the requirements of small size. 


SECRET 


w 




146 


ELECTRONIC CONTROL SYSTEMS 


2. It required no slip rings or commutators. 

3. Its use of a simple solid metallic rotor 
suited it to operation at high rotational speeds. 

4. It facilitated the regulation of supply volt- 
ages over a wide range of rotational speeds by 
electric means, since the generated emf was 
directly related to rotational speed in both fre- 
quency and amplitude. 

5. It was well adapted to quantity production 
by conventional methods. 

Extremely scanty information was available 
in the technical literature on design principles 
for permanent magnet alternators. These had 
previously been used to a limited extent as in- 
dustrial tachometers, as magnetos, and as spe- 
cial purpose generators. 214 The attainment of 
the power-to-volume ratio required for the fuze 
generator depended upon the use of relatively 
new magnetic materials and the extremely high 
rotational speeds involved. 

The feasibility of the permanent magnet 
alternator was proved by exploratory investi- 
gations at the National Bureau of Stand- 
ards. 4 - 18 Early models of generator-powered 
fuzes were designed by the Westinghouse Elec- 
tric and Manufacturing Company, and engi- 
neering design of the generator used in produc- 
tion fuzes was done by the Zenith Radio Cor- 
poration. 19 

1. Principles of operation of the alternator. 
The principles of operation of the permanent 
magnet alternator were easily derived for a 
highly idealized case and with several simplify- 
ing assumptions. The complete and rigorous 
mathematical analysis, including the effects of 
nonlinearity in the magnetic circuit and in the 
rectifier and hot filaments which constituted 
the coupled loads, was not attempted. If the 
solution were actually possible, its value is not 
consistent with the labor demanded. The ideal- 
ized solution was fully adequate for evaluating 
the parameters of generator operation and for 
indicating the principles upon which a straight- 
forward experimental development could be 
based. 

A conventionalized diagram, applicable to the 
permanent magnet alternators which were used, 
is shown in Figure 66. The rotor, a six-pole per- 
manent magnet disk, is located centrally within 
the magnetic stator which carries the arma- 


ture windings. The magnetomotive force of the 
magnet passes flux through the stator to link 
each of the armature turns, and for each 60- 
degree rotation this flux is reversed in polarity. 
The resulting emf in the armature coils com- 
pletes one electric cycle for each 120 degrees 
of rotation. 

In the analysis which follows the six-pole 
alternator is considered as the equivalent of 
three series-connected bipolar alternators op- 
erating at three times the actual rotational fre- 



Figure 66. Diagram of six-coil generator. 
Rotor, stator, and armature windings are shown. 
Location of magnetic poles on rotor and flux 
paths are indicated. 

quency. Each bipolar alternator carries an 
armature winding of (N/ 3) turns, where N is 
the total number of turns for the six-pole alter- 
nator. Each bipolar magnet develops magneto- 
motive force M equal to that developed by an 
adjacent pair of poles on the six-pole rotor. The 
permeance P m for the rotor-stator flux linkage 
corresponds to that for an adjacent pair of 
poles in the six-pole alternator, i.e., two of the 
six rotor paths in shunt, two of the six stator 
paths in shunt, and two air gaps in series. 

Experiment indicated that an alternator of 
this type delivered an essentially sinusoidal 
current 7 into a load containing only linear ele- 
ments. The generating flux <f> was then sinus- 
oidal. The stator saw the rotor as a sinusoidally 


SECRET 


POWER SUPPLIES 


147 


varying mmf M of internal reluctance inde- 
pendent of angular position. 

Thus, neglecting phase, 

I = /max e**, 

</> = 0max (40) 

M = M max e jwt j 

where w = 2nf (electrical) — 6 jt/ (rotational). 
The total flux linking an adjacent pair of arma- 
ture coils with their pair of rotor poles is due to 
the rotor mmf and to the current in the coils 
themselves. 


<t> = MP m + (P m + P,), (41) 

where P m is the effective permeance of the mag- 
netic path through magnet, air gaps, and stator 
(two poles) . Pj is the leakage permeance of the 
stator (two poles). N is the total armature 
turns. 

The emf generated in the armature is 

E =~kN% (42) 


where k, a proportionality factor, is equal to 
10~ 8 , and introducing equation (40), 

E = —jkNw<l), (43) 

combining with equation (41), 

E = —jkNw | ~MP m + (P„ + p,)J. (44) 


The term E drives the current / through the 
internal resistance of the armature coils R if and 
the external load, 


Z Q = R o + jX o, 

E = I{Ri + Ro + jX 0 ) 

combining with equation (44), 


(45) 


I(Ri + + jX 0 ) 

= -jkNw | ~MP m + 0 ' 4 y— (P m + P,)J, 

j = -jkMPmNw 

Ri+R 0 +j ^^~ (P m +P/)+X 0 J 

| 7 | kM m ax Pm X w 

| J- max | — 1 = 

^R i+Ro y+^AMPw (Pm+Pi)+Xo J 

(46) 


In practice X 0 was always capacitative. At 
higher frequencies, the current approaches the 
limit. 


| /max | 


SM r 


OAN P m + P ’ 
which may also be written 

I t | /0max-A 


(47) 

(48) 


From the foregoing it is apparent that with 
increasing frequency the alternator becomes a 
constant current source which will supply a 
constant voltage to a load of fixed resistance. 
The limiting maximum value of current is, by 
equation (48) , directly proportional to the rotor 
flux linkages with the stator turns and inversely 
proportional to the total generator inductance. 
By equation (47) the limiting current is in- 
creased by increase in M (the rotor mmf) or 
by increase in P m (the rotor path permeance), 
but is decreased by increase in N, since this 
gives a square law increase in the inductance 
and only a first-power increase in rotor flux 
linkages. 

While leakage permeance contributes no 
power producing flux linkage, it is seen from 
equation (46) to be as effective as rotor perme- 
ance in increasing the rate at which current 
constancy is approached with rising frequency. 
For increasing this rate R 0 and R i should be 
held to minimum permissible values. 

The internal resistance R t contains three 
series components : the resistance of the stator 
turns, the reflected resistance of stator and 
rotor hysteresis loss, and the reflected stator 
and rotor eddy-current loss. The reflected re- 
sistances both increase as the square of the fre- 
quency. 217 It is obviously important to minimize 
them, since they represent power losses which 
impair rather than help regulation of load volt- 
age with frequency. 

In practice the design of the magnetic circuit 
of the generator was worked out to provide 
some excess of power at the minimum rota- 
tional speed. Subsequent adjustment of coil 
turns, bleeder circuit components, and the rotor 
magnet strength achieved the proper output 
voltages and regulation characteristics. 

2. Voltage regulation. The permanent mag- 
net alternators of production design were es- 


1 SECRET 


I 


148 


ELECTRONIC CONTROL SYSTEMS 


sentially self-regulating with frequency, pro- 
vided they were heavily loaded. However, the 
voltage regulation was improved by the addi- 
tion of capacitative reactance to the load cir- 
cuit. 22 This was done by either a series or a 
shunt connection. The methods were used indi- 
vidually or in combination. 

Series connection may be evaluated from 
equation (46) of the preceding section. With 
X 0 negative the total reactance goes to zero at 
some frequency and the generator current is 
limited entirely by the circuit resistance. The 
value of C could be chosen to produce current 
resonance just at the lowest operating fre- 
quency so that transition into current, and 
voltage, constancy was made more sharp. If C 
were too small for the values of L and R, the 
high Q of the circuit at resonance caused over- 
regulation. With too large a value of C the en- 
tire effect was lost. 

Shunt regulation was obtained by shunting 
the generator output with a mesh consisting of 
a resistor and a capacitor in series. The values 
were so chosen that the mesh loaded the gen- 
erator only slightly to the threshold operating 
frequency but loaded increasingly with increas- 
ing frequency. Analysis indicated that this cir- 
cuit was inherently overregulating if C were 
too great and R were too small. 

The discussion to this point has considered 
the voltage regulation of a single supply volt- 
age from a single generator winding, the high- 
voltage supply. The filament winding was regu- 
lated, however, by reaction from the high-volt- 
age regulation since it was closely coupled to 
the high-voltage winding with an iron core in 
common. The coupling was not 100 per cent and 
consequently the cross-regulation was not per- 
fect. It was usually necessary to maintain B 
voltage with slight overregulation in order to 
develop adequate A regulation. Early develop- 
ment model generators achieved good cross 
regulation by locating the coils in the flux field 
so as to produce a phase asymmetry in their 
voltages. 22 This was abandoned in production 
models to simplify the mechanical design of the 
generator. 19 The C bias voltage was inherently 
regulated with the B supply, since it was de- 
veloped as an IR drop in the plate current cir- 
cuit. 


Representative A and B voltage rotational 
speed regulation characteristics are shown in 
Figure 67. Shunt regulation circuits for fuzes 
T-50, T-51, and T-30 are shown in Figures 75, 
76, and 77. Series regulation as used in fuze 
T-132 is shown in Figure 78. Here the series 


1.5 

3 

S £ 1.4 

5 -j 

Si 

m 1.3 

Figure 67. Plate and filament supply voltages 
versus rotational speed of generator in T-51 
fuze. Dashed curve A is for filament voltage. 
Solid curve B is for plate voltage. (Reference 
209.) 

capacitance was provided by the capacitors of 
the bridge-type voltage-doubling rectifier. Com- 
pound regulation, i.e., shunt and series capacit- 
ance, was used in fuze T-82 as shown in the 
circuit of Figure 79. 

3. Rotor design. The magnetic rotor has been 
considered in the case of an ideal generator as 
a source of sinusoidally varying mmf having 
constant internal reluctance. The rotor of an 
actual generator does behave much in this man- 
ner, as can be seen by reference to Figure 68, 
the major hysteresis loop for the magnetic ma- 
terial constituting the rotor. 68 A rotor in its 
matching magnetic stator (such as is shown in 
Figure 66) operates on a minor hysteresis loop 
4-5 while in rotation. The minor loop lies with- 
in the third quadrant of the major loop specifi- 
cally located according to the magnetic precon- 
ditioning of the rotor. Its slope in any event is 
very nearly equal to that of the major loop at 
point 2. 215 The rotor, for any angular position, 
has an operating point at the intersection of the 
minor loop with an appropriate shear line. The 
shear line is a radius vector whose negative 
slope equals the ratio of permeance of the space 
occupied by the magnet to permeance of its ex- 
ternal flux path. The end points of the minor 
loop lie on the two shear lines 0-6 and 0-7, 
which represent respectively maximum exter- 
nal permeance (the angular position for align- 
ment of rotor and stator poles) and minimum 
external permeance (the mid-position of com- 
plete misalignment). 



ROTATIONAL SPEED (RPM*I0 3 ) 



POWER SUPPLIES 


149 


The axis of the minor loop 4-5 must pass 
through point 3, which is the intersection of the 
major loop with shear line 0-3. Shear line 0-3 
corresponds to the minimum external perme- 
ance to which the magnet has been exposed. 
Where rotors have been removed from a mag- 
netizing jig and transferred openly to the gen- 
erator, 0-3 corresponds to free-space permeance 
and is the strongest demagnetizing force the 
rotor can encounter except for the application 
of a demagnetizing field from external current 
turns. 



Figure 68. Diagram of magnetic operating 
cycle for material constituting generator rotor. 
Outlying curve is major hysteresis loop for ma- 
terial. Operation is on minor loop 4-5. 

If the axis of the minor loop is extended to 
intersect the H axis, point 8 gives the value of 
virtual field intensity of the magnet. This value 
multiplied by the effective length of the magnet 
is the M (maximum mmf) of equation (40). 
The slope of the axis of minor loop 4-5 defines 
p eff , the effective internal permeability of the 
rotor material. Together with the effective 
length and cross section of the rotor magnet 
this determines the internal reluctance of the 
magnet. This reluctance, the air gap reluctance, 
and the stator reluctance determine P m (rotor 
path permeance for two adjacent poles) of equa- 
tion (41). 

For a rotor advance of 120 degrees the stator 


sees one full cycle of sinusoidal mmf but the 
rotor meanwhile twice traverses its unidirec- 
tional loop of operation. At point 5 in the loop 
the stator sees 0 mmf. At point 4 it sees a maxi- 
mum mmf, either positive or negative accord- 
ing to the sense of rotor-stator pole alignment. 
The minor loop 4-5 defines rotor operation in 
the unloaded generator. With a load applied the 
rotor magnet is linked by armature current 
turns and is subjected to an additional demag- 
netizing force which shifts the loop down and 
along its axis by an amount dependent upon 
the phase and magnitude of the load current. 
The use of high coercivity magnetic material, 
such as an Alnico, is indicated if this effect is to 
be minimized. 

In the design of the generator, spatial con- 
siderations dictated a maximum rotor diameter 
of approximately 1 in., which, for six-pole mag- 
netization, set 0.5 in. as the length of each 
magnet. The minimum radial gap between 
rotor and stator poles for quantity production 
was set at 0.010 in., with gaps of 0.020 in. or 
more considered preferable. The maximum per- 
meance shear line could be roughly estimated 
to have a negative slope of 25 in the case of the 
0.010-in. gap, and 12.5 in the case of the 0.020- 
in. gap. Reduction of the effective air-gap area 
by reduction of stator pole thickness would 
further reduce the slope of the shear line. 

Permanent magnet steels are used most effi- 
ciently at an operating point which puts their 
EH product at a maximum. This corresponds 
very nearly to operation with a shear line hav- 
ing negative slope equal to the ratio of residual 
induction to coercivity for the material. 215 For 
Alnico I this ratio is 16; for Alnico II, 13; for 
Alnico IV, 7. All were tried as rotors during 
the experimental program. Alnico IV proved 
magnetically superior and was used universally 
in the production generators. Cast rotors of 
Alnico IV also proved mechanically stronger 
than cast rotors of other Alnico types. 

Salient pole rotors, like that in the develop- 
ment model generator of Figure 69, were tried 
as a means of increasing the effective length of 
the rotor magnets. When magnetized by con- 
ventional means, the internal magnetic paths 
apparently jumped the tooth spaces between 
poles, so that the benefit was not realized. 45 




150 


ELECTRONIC CONTROL SYSTEMS 


Since they were mechanically weaker and less 
well balanced than the simple disk rotors, their 
use was abandoned. 

The proper selection of the A to B turns ratio 
for the armature coil permitted the supply of 
precisely proportioned A and B voltage 
through average rectifiers to nominal loads. 
The B/A ratio could be held within tolerable 
limits (7 per cent) when rectifier, filter, and 
load components were allowed their contingent 



external coil or by the passage of alternating or 
direct current through the armature winding. 
By reference to Figure 68, it is seen that the 
demagnetizing force moved the operating point 
of the magnet along its minor loop to the inter- 
section with the major loop at point 3. Further 
demagnetizing force moved the operating point 
down the major loop. When the demagnetizing 
force was removed the magnet assumed a new 
minor loop on an axis parallel to, but below, its 
former axis and with operating end points on 
its former shear lines. 

The demagnetization produced a stabiliza- 
tion of the magnet against the effects of demag- 
netizing forces from momentary overload, etc. 
The farther displaced its operating minor loop 
from the major loop the greater was the mar- 
gin of protection. Since the great percentage of 
production generators required strong demag- 
netization, their operation in service showed 
no fatigue effects nor pole shift. 

Production Models. The production model of 
the basic six-coil generator, for use in nose- 
mounted vane-type fuzes, is shown in Figure 
70. An Alnico IV rotor in the form of a disk, 
1.020 in. OD and 0.25 in. thick was used. The 
stator core was a stack of five punched lamina- 
tions of 26 gauge (0.0188 in.) low-silicon audio- 
transformer steel, C grade. The radial air gap 
between rotor and stator was 0.010 in., which 


Figure 69. Early experimental generator. 
Three-section stator and thick salient pole rotor 
are shown. 

of spread. However, the variation of magnetic 
strength in individual saturated rotors, al- 
though it produced no effect in the B/A ratio, 
caused a spread of over 20 per cent in the com- 
mon level of the voltages. 08 This spread was 
eliminated by designing the generator to de- 
liver voltages of the required or greater value 
with all saturated rotors except a small per- 
centage of the weakest. After the assembly of 
the entire power supply the rotors were demag- 
netized individually to provide the proper oper- 
ating voltages. 

The demagnetizing field could be applied by 



Figure 70. Production model six-coil generator 
and principal components. Assembled generator 
is shown at left. Rotor, mounted stator, and cover 
plate are shown at right. 

was maintained at +0.0030 to —0.0015 in. in 
production by careful control of the dimensions 
of the die cast housing and its seats for the ball 
bearing assemblies. The maximum dimensions 
of the housing were 2.75 in. for the diameter 


POWER SUPPLIES 


151 


and 0.75 in. for the thickness, exclusive of shaft 
extensions. 

Although three coils would have been ade- 
quate for intercepting all the flux of the mag- 
netic circuit, small coil dimensions were pos- 
sible when six were used. This permitted a re- 
duced length of mean turn and a thinner gen- 
erator assembly. Each coil was wound on a 
plastic bobbin with a high-voltage winding of 
1,940 jumbled turns of No. 41 AWG enameled 
copper wire. Over this was the filament wind- 
ing of 13 turns of No. 28 AWG Formvar-coated 
copper wire. The six B and the six A windings 
were connected respectively in series. 

In operation the generator developed open- 
circuit voltage in the plate winding which in- 
creased linearly with rotational speed to ap- 
proximately 1,000 v at 40,000 rpm. This indi- 
cated the absence of appreciable core loss in the 
magnetic circuit. 19 The power output into rated 
loads with an average saturated rotor was ap- 
proximately 10 w at 15,000 rpm. This provided 
an adequate margin for accepting a high per- 
centage of rotors after voltage had been stand- 
ardized by demagnetization. 

A second production-model generator for use 
in the nose-mounted vane assembly was the 
single serpentine coil model shown in Figure 
29 of Chapter 6. This was developed as a means 
of reducing the production complexity of the 
six-coil generator by the use of a single pliant 
bundle wound coil which could be intertwined 
about the stator pole extensions. The coil was 
impregnated with varnish and baked in its final 
deformed position on the stator. The flux link- 
age with the serpentine coil is identical with 
that of the six-coil generator, each of three 
circumferential sections of the single coil being 
linked by a complete flux path in the one case 
and each of three pairs of series coils being 
linked by a complete flux path in the other. 

The rotor was an Alnico IV disk, 1.178 in. 
OD and 0.25 in. thick. The stator core was a 
stack of seven laminations of 0.075-in. low-sili- 
con transformer steel, C grade. A rotor-stator 
air gap of 0.020 in. was possible here by virtue 
of the increase in rotor diameter and in thick- 
ness of the stator pole face. The generator was 
assembled into a case consisting of two drawn 
brass cups. Maximum dimensions were ap- 


proximately 2.85 in. for the diameter and 0.75 
in. on the axis, exclusive of shaft extensions. 

The serpentine coil included 2,700 turns of 
No. 39 AWG Formvar-coated copper wire for 
the B winding and 21 turns of No. 28 AWG 
Formvar-coated copper wire for the A winding. 
The electric operating characteristics were 
essentially equal to those of the six-coil gen- 
erator. 

Miniature mortar fuze T-132 used the stand- 
ard six-pole generator with mechanical modifi- 
cations for adapting the stator assembly to a 
maximum 2 in. OD and for incorporating the 
rotor into a single unit with the driver turbine. 
This is shown in Figure 42 of Chapter 4. The 
reduction in OD of the stator assembly was 
effected by removal of peripheral sections of 
the lamination stack which had been used for 
mounting the stator. The magnetic operation of 
the stator was not significantly affected. The 
rotor was reduced in diameter to 1.000 in. with 
a resultant increase in radial air gap to 0.018 
in. The consequent reduction in generator out- 
put relative to the standard six-pole model was 
corrected by appropriate revision of the recti- 
fier and load circuits. 

In a similar way the miniature mortar fuze 
T-171 adapted the serpentine coil generator to 
turbogenerator use. The rotor and the stator 
lamination stack were in this case identical to 
those used in T-132. For forming the serpen- 
tine coil on a small radius and holding axial 
thickness to the permissible maximum the 
winding was distributed in two coils. The re- 
sulting double serpentine is shown in Figure 
35 of Chapter 4 in comparison with the single- 
coil model. 

The generator for miniature mortar fuze 
T-172 used three coils and a multisection stator 
core in a novel design evolved by the Zenith 
Radio Corporation. The production model was 
superficially similar to the development stator 
assembly 1 shown in Figure 45 of Chapter 4. 

The production stator was a 0.125-in. stack 
of fine transformer steel laminations in the 

1 This development stator shows the pole piece ring as 
continuous. Magnetic isolation of the six “pole pieces” 
was effected by shading the ring at the six intermediate 
points with copper straps. The production model was 
superior to this model both in operational characteristics 
and in simplicity of construction. 


152 


ELECTRONIC CONTROL SYSTEMS 


shape of a ring 2.00 in. OD and carrying three 
radial magnetic paths with wide pole faces on 
an ID of 0.820 in. Three additional radial ele- 
ments with wide pole faces were preassembled 
as stacks, upon which coil bobbins were molded 
and the coils wound. These coil : on-core assem- 
blies were riveted into the stator ring to com- 
plete the stator magnetic circuit. A retainer 
ring carrying six lugs was used to brace the 
pole piece “ring” and index adjacent poles for 
circumstantial air gaps of 0.050 in. The re- 
tainer was a nonmagnetic alloy (Advance) of 
high resistivity for minimizing eddy-current 
loss. 

The rotor was an Alnico IV disk, 0.780 in. 
OD and 0.250 in. thick. This provided a rotor- 
stator air gap of 0.020 in. The large stator pole 
width permitted a reasonably steep shear line 
for rotor magnet operation even with the small 
diameter rotor. Consequently, the electric 
characteristics of this generator were similar 
to those of other mortar fuze generators. 

Bomb fuze T-82 used a turbogenerator seated 
in the base casting which threaded into the 
fuze well. (See Figure 58.) This limited the 
OD of the generator to 1.33 in. and its axial 
length to about the same value exclusive of 
shaft extensions. A satisfactory design to the 
space requirements was achieved in conjunc- 
tion with a single-bobbin wound coil by a 
drastic revision of the magnetic circuit. 

The serpentine coil generator used a mag- 
netic circuit (involving three pairs of poles) 
which was restricted to one plane. The winding 
was deformed from the plane to thread alter- 
nately over and under adjacent stator poles. 
Alternately the winding could have been held 
in one plane and the magnetic circuit folded 
around the coil. The T-82 generator, which is 
shown with its disassembled components in 
Figure 71, used a magnetic circuit which folded 
around the coil and brought six stator pole 
pieces of alternate polarity into alignment with 
those of a magnetic rotor located coaxially at 
the end of the coil. Despite its unconventional 
magnetic circuit design, the T-82 had an elec- 
tric and magnetic operating cycle identical with 
that of the serpentine or six-coil generator. 

The principal components of the magnetic 
stator were a cup with three extended poles, a 


spider with three extended poles, and an annu- 
lar magnetic core which linked the cup and 
spider through the center of the coil. The cup 
and spider were drawn from a 0.062-in. sheet 
of 47 per cent ferronickel. The core was turned 
from first quality ingot iron. 


Figure 71. T-82 generator and principal com- 

ponents. Assembled generator is shown at left. 
Grouped at right are spider, coil, core, rotor, 
center stud with upper bearing, cup with cover 
plate. 

The success of this generator design hinged 
on the use of 47 per cent ferronickel in the 
magnetic stator. It was used unannealed after 
drawing and still had extremely high permea- 
bility and low hysteresis losses at the low 
(2,500 gauss) flux densities encountered. In 
addition, its high resistivity was of extreme 
importance in reducing eddy-current losses to 
a negligible value in an unlaminated assembly. 

The magnetic rotor was a disk of Alnico IV, 
1.140 in. OD and 0.400 in. thick, magnetized 
with six peripheral poles. The radial gap be- 
tween rotor and stator was 0.030 in. The large 
air gap gave a very low slope to the shear line 
for the rotor magnet with consequent poor utili- 
zation of the magnet volume. This necessitated 
the use of the thick rotor. The coil bobbin car- 
ried a jumble winding of 3,800 turns of No. 42 
AWG enameled copper wire for the high-volt- 
age supply and over this 28 layer wound turns 
of No. 28 AWG Formvar copper wire for the 
filament supply. 

Because of its long magnetic circuit, the T-82 
generator was characterized by high leakage 
inductance which limited the power available 
into the operating load to 7 w with a saturated 
rotor at 20,000 rpm. For this reason a com- 
pound regulating circuit was used to assure 




POWER SUPPLIES 


153 


adequate operating voltages when marginally 
weak magnetic rotors were used. The high leak- 
age inductance also gave a large value of volt- 
age-load regulation. In consequence the T-82 
rotor was demagnetized to standard output 
voltage after final assembly of the fuze when 
the generator operated into its actual load. 

A novel experimental generator was devel- 
oped as a standby for use in the T-82 fuze-well 
mount. This used a stator of stacked lamina- 
tions and a coplanar coaxial disk rotor of small 
diameter. However, the stator carried a single 
distributed winding of 90 turns of No. 20 cop- 
per wire. By use of a rotor 0.5 in. thick and an 
air gap of 0.010 in. a power output of 13 w at 
20,000 rpm was delivered at 6 v. This was fed 
to an externally located miniature transformer 
whose secondaries supplied the required A and 
B voltages. 

The turbine-driven generator of the P-4 ex- 
perimental bomb fuze differed both in design 
and operating principle from other genera- 
tors. 204 In this case both permanent magnet and 
armature coils were stationary. The emf was de- 
veloped by passage of pulsating flux through 
the coil core under the control of a highly per- 
meable salient pole rotor which while in rota- 
tion served as a periodically varying reluctance 
in the magnetic circuit. 

The general assembly can be seen in Figure 
72. The two coils carrying distributed A and B 
windings were mounted on the legs of a U- 
shaped lamination stack which was eccentri- 
cally located relative to a laminated rotor hav- 
ing seven salient poles. A yoke containing the 
permanent magnets linked the base of the 
U-shaped coil core to the rotor through a wide- 
angle pole face which saw one pole of the rotor 
for any angular position. The two poles of the 
coil cores were designed for an angular separa- 
tion of one and one-half teeth of the seven-pole 
stator. Thus the rotor in rotation alternately 
passed unidirectional flux through the two coils 
at a frequency of 7 cycles per revolution and 
with 180-degree phase difference. The coils 
were series-connected to deliver alternating 
current at 7 times rotational frequency. 

With its 36-blade 45-degree blade-angle metal 
turbine the generator operated at 9,000 to 30,- 
000 rpm for airspeeds of 300 to 1,000 fps, so 


that the generator emf was in the range of 
1,050 to 3,500 c. In this range the generator 
was regulated by its own inductance and no 
external regulation circuit was required. Be- 
cause of the use of stationary magnets it was 
possible to effect normalization of output volt- 
age by use of an externally adjustable magnetic 



Figure 72. P-4 power supply, partly disassem- 

bled. Stator and its two armature coils can be 
seen at right edge of generator assembly. (Photo- 
graph by Bell Telephone Laboratories.) 

shunt. The voltage and power delivered by the 
P-4 generator was approximately equal to that 
delivered by the rotating magnet designs. 


34 6 Rectifier System 

A rectifier was required for converting the 
alternating high-voltage output of the genera- 
tor to direct current for supplying the plate 
circuit of the fuze. Filaments could be operated 
on alternating current directly from the gen- 
erator A winding as discussed in Sections 3.1 
and 3.2. The B-supply rectifier was necessarily 
of an electronic type, since the intermittent con- 
tacting of mechanical rectifiers was an intoler- 
able source of r-f disturbance. Thermionic di- 
odes and blocking layer cells, both selenium 
and copper oxide types, were considered as 
rectifiers. 

Full-wave rectification was a virtual neces- 
sity in order to minimize ripple and obtain a 
satisfactory voltage conversion from such a 
high-impedance source as the generator B 
winding. Three types of full-wave connection 
were possible : full wave with two diodes work- 


SECRET 


154 


ELECTRONIC CONTROL SYSTEMS 


ing from a center-tapped supply, two diodes in 
a bridge or cascade voltage doubler, four 
diodes in a full-wave bridge. 

Vacuum-Tube Rectifiers. No existing tubes 
of the subminiature class were readily suited 
to this service. Triodes NR3 and NS3 had ade- 
quate current capacity and inverse voltage 
characteristics. 62 However, they were required 
in multiple, and separate electrically isolated 
filament supplies were required because the 
cathodes were directly heated. 

Blocking Layer Rectifiers (Selenium and 
Copper Oxide). Selenium or copper oxide cells 
rectify by preferential conduction in one sense 
of direction across an interface, between sele- 
nium and iron in the one type of cell and be- 
tween copper and copper oxide in the other. 
Having no filaments, assemblies of these cells 
could be used in any of the full-wave circuits 
without need for isolated filament supplies. Be- 
cause of this simplicity of application and the 
indications that a selenium rectifier cell of 
acceptable characteristics was feasible, 216 ex- 
tensive effort was directed toward the develop- 
ment of such a rectifier and the effectuation of 
facilities for its production in quantity. This 
program, which was carried on with close co- 
ordination between the National Bureau of 
Standards and the several manufacturers, was 
largely a program of production engineering 
and quality control. It is discussed in more de- 
tail in Chapter 6. 

The selenium cell shown in Figure 29 of 
Chapter 6 was developed as the basic component 
for all the power supply rectifiers. An assembly 
of 20 cells in a full-wave bridge is also shown. 
Other production assemblies were a 24-cell full- 
wave bridge and a center-tapped 20-cell stack 
for use as a bridge doubler. The individual cells 
were 0.28 in. in diameter and 0.030 in. thick. 
The effective rectifying zone was a central circu- 
lar area of 0.075 sq in. A typical static voltage- 
current characteristic for the selenium cell is 
shown in Figure 73. For comparison the static 
characteristics of a type-AQ copper oxide cell 
of similar dimensions is included. 

Although the cells had nonlinear character- 
istics for both forward and reverse current, 
values of effective forward or reverse resist- 
ance could be defined for any static operating 


point as the simple ratio of E to I. Similarly a 
value of effective resistance could be ascribed 
to a group of several series-connected cells for 
specified operating conditions. A full-wave 
bridge (cf. Figure 75) comprising four sym- 
metrical arms, each arm of forward resistance 
R f and reverse resistance R b , could be approxi- 
mately represented 62 by a full-wave bridge con- 
taining four ideal rectifiers, having a resistance 
2 R f in series with the load and a resistance 
(R b /2) in parallel with the source. 

This clearly shows the significance of both 
forward and reverse characteristics of the cells 
in determining the output voltages, particularly 
when a high source impedance is used. In the 
fuze power supply the B winding was a high- 
impedance source tightly coupled to the A sup- 
ply. Here a decrease in the effective R b of the 
bridge loaded the B winding more heavily and 
by reflection loaded the A winding. Conse- 



Figure 73. Static characteristics of blocking 
layer rectifier cells, 7 mm in diameter. Curve Se 
is for selenium cell. Curve AQ is for type AQ 
copper oxide cell. Data from reference 64. 

quently both A and B voltages decreased. An 
increase in R f decreased the B voltage but light- 
ened the load on generator so that the A voltage 
increased. 

In the development study which was prima- 
rily the statistical analysis of extensive experi- 
mental data, measurements were made on the 
static characteristics of individual cells. Recti- 
fiers assembled from cells of known character- 
istics were then studied in dynamic service, i.e., 
operating with typical generators under typical 


SECRET 


POWER SUPPLIES 


155 


loads. The resulting correlation 65 between static 
cell characteristics, observed under selected ref- 
erence conditions, and operating power supply 
output voltages is shown graphically in Fig- 
ure 74. The limits within which individual cells 
were classified for acceptability are shown by 
dashed lines in the figure. 15 

Subsequently a dynamic test on 60 c alter- 
nating current was evolved 68 with proper limits 
for the assembled rectifier bridges. It was found 
that statistical assurance of an acceptable 
bridge resulted from a distribution of 75 per 
cent or more of the individual cells in Class A, 
95 per cent or more in Classes A, B, and C, with 
no open cells in the remainder. 


selenium cells output voltages could be main- 
tained within tolerable limits 15 over the re- 
quired operating range of —40 to +60 C. 192 
Copper oxide cells were not suited to use in the 
power supply because both forward and reverse 
resistances showed a marked inverse variation 
with temperature. This resulted in the develop- 
ment of excessive A voltage at extreme low 
temperature. 64 


3,4,7 Filter and Detonator Firing System 

The term filter system was used broadly to 
include the several elements of resistance and 



0 1 2 3 4 5 6 

VOLTS FORWARD DROP PER CELL AT 20MA 


Figure 74. Power supply output voltages as function of static characteristics of selenium cells in the 
rectifier. Curves A refer to indicated values of filament voltage. Curves B refer to indicated values of 
plate voltage. Dashed lines indicate acceptance limits for cells of Classes A, B, and C. The diagram is 
from reference 68. 


Selenium cells had appreciable temperature 
dependence. The reverse resistance was a maxi- 
mum in the 20 to 30 C range and decreased for 
higher or for lower temperature. 206 The forward 
resistance varied in approximately inverse re- 
lation to the temperature. Reverse resistance 
decrease, particularly at lower temperatures, 
was of primary importance in affecting the 
output voltages from the power supply. 69 With 


capacitance interposed between the rectifier 
and the power-supply output terminals. The 
system served the following purposes: reduc- 
tion of ripple voltage in the plate supply, de- 
velopment of the required C bias potentials, 
storage of charge for firing the detonator, pro- 
vision for adjustment of output voltage by the 
insertion of selected resistors, and provision of 
an electric arming delay where required. 


% SECRET 



156 


ELECTRONIC CONTROL SYSTEMS 


The power supply filters in all cases em- 
ployed an input capacitor followed by a single 
L section of series resistance and shunt capaci- 
tance. Since the input capacitor was fed recti- 
fied pulses from the high-impedance B winding 
of the generator through a relatively high-re- 
sistance rectifier, it contributed materially to 
ripple reduction. As a class the filters operated 
with about 1 v of ripple across the input ca- 
pacitor and 100 mv of ripple across the B volt- 
age output at 1,500 c. This ripple frequency 
corresponded to a generator speed of 15,000 
rpm, the minimum required for operation. At 
higher frequencies the ripple attenuation was 
proportionately greater. 

The C bias potentials for thyratron and am- 
plifier were developed across a resistor in the 
negative leg of the power supply filter. A single 
voltage of approximately —7.5 v was adequate 
for those fuzes having high-resistance grid cir- 
cuits in their amplifiers. Here the full-bias 
voltage was applied to the thyratron grid and 
a high-resistance voltage divider contained in 
the amplifier supplied approximately —1.5 v to 
the amplifier grid. In fuzes T-51 and T-82 which 
used low-resistance amplifier grid circuits, sep- 
arate resistors in the negative leg of the filter 
provided the two bias voltages. 

Due to the steep load-regulation character- 
istics of the power supply an undesirable spread 
in output voltages would result from the nor- 
mally encountered spread in the plate current 
demands of the tube complements. In produc- 
tion, bleeder resistors were selected to bring 
each power supply to very nearly a standard 
load condition. This is discussed in detail in 
Chapter 6. 

The requirements upon the output filter ca- 
pacitor for service in detonator firing and in 
delayed arming have been treated in Section 3.3. 


Power Supply Circuits 

Representative circuits for several power 
supplies are shown in Figures 75, 76, 77, 78, 
and 79. Values for the circuit components are 
included. 

The basic power supply was the T-50 model 
of Figure 75. A typical T-50 assembly is pic- 


tured in Figure 26 of Chapter 6. The limits for 
acceptable operating characteristics are sum- 
marized in NDRC specification for power sup- 
ply PS-1. 17 



Figure 75. Schematic diagram of power supply 
of T-50 fuze. 


The T-51 power supply of Figure 76 differed 
from the T-50 chiefly in respect to the C-bias 
circuit. Here a low-resistance source of ampli- 
fier bias was additionally provided. 



Figure 76. Schematic diagram of power supply 
of T-51 fuze. 


The T-30 (T-2004) power supply is shown in 
Figure 77. This differed from the T-50 supply 
in that the detonator firing capacitor C20 was 


COORDINATION OF ELECTRIC DESIGN 


157 


charged through a resistor R27 to provide an 
electric arming delay. 

The T-132 (T-171, T-172) power supply is 
shown in Figure 78. This used a bridge-type 
rectifier doubler. The doubled voltage was de- 
veloped across capacitors C23 and C24, as 


B+ G C- A- A+ TP 



Figure 77. Schematic diagram of power supply 
of T-30 fuze. 


shown. Voltage adjustment was effected by 
selection of series dropping resistor R35 and 
bleeder resistor R29. Electric arming delay was 
provided by the use of resistors R27 and R28 
in connection with detonator firing capacitor 
C20. 

The T-82 power supply is shown in Figure 79. 
This featured the use of compound regulation 
provided by C15, C17, and R19. A low-resist- 
ance bias supply for both thyratron and ampli- 
fier grids was provided by resistors R7 and R14. 


ments involved many considerations which 
generally required compromise to make them 
mutually compatible. The one overall consider- 
ation was the military requirement for per- 
formance: the fuze must detonate a particular 
missile or group of missiles when the fuzed 
rounds were in a specified space region with 
respect to the target. Along with this prime 
requirement were generally a host of second- 
ary requirements, such as (1) the fuze must 
occupy a predetermined position on the round 
and must fit a fuze well whose dimensions are 
fixed; (2) the space allotted to the electronic 
components was determined by mechanical con- 
siderations which govern shape and volume; 
(3) conditions of use which include temper- 
ature, humidity, high-altitude operation, and 
storage life; and (4) special electrical features 



Figure 78. Schematic diagram of power supply 
of T-132 fuze. This is the same as that for fuzes 
T-171 and T-172. 


3 5 COORDINATION OF ELECTRIC DESIGN^ 

3,5,1 The Coordination Problem 

The design requirements for the various sub- 
assemblies of radio proximity fuze were deter- 
mined on the basis of somewhat arbitrary deci- 
sions concerning expected performance for each 
part of the fuze. Coordination of these require- 


relating to time of activation, circuit switching 
for arming or self-destruction, and simultane- 
ous use of a quantity of fuzed rounds without 
mutual interference. Mechanical design is dis- 
cussed in Chapter 4 ; it will be referred to here 
only with respect to the limitations which me- 
chanical problems imposed on electric design. 

A logical method of discussing design coor- 
dination is to separate the fuzes according to 
intended application (antiaircraft or ground 
approach) and also according to the type of 
missile on which they were to be used (bombs, 
rockets, or mortars). However, in the actual 


j This section was prepared by the editor with the aid 
of W. S. Hinman, Jr., Chief Engineer of the Ordnance 
Development Division, National Bureau of Standards. 


SECRET 


158 


ELECTRONIC CONTROL SYSTEMS 


course of development during World War II, 
each fuze, regardless of its application, was 
built largely on experience and -designs which 
accrued from previous work. The factors in- 
fluencing design depended so much on the state 
of the art that for the following discussion a 
chronological order is preferable. The presen- 
tation will be simplified by confining the discus- 
sion to the major projects. 

Since one of the objectives of this section is 
to tie together the preceding four sections of 
the chapter, frequent references to these sec- 


B+ PENTOOE C- A+ TP 



Figure 79. Schematic diagram of power supply 
of T-82 fuze. 


tions and other chapters in the volume will be 
necessary. The reasons for concentrating on 
doppler-type radio fuzes have been discussed in 
Section 1.2, and those reasons will not be re- 
peated here. 


Battery-Powered Rocket Fuze 

The T-5 fuze for the M-8 rocket was devel- 
oped for antiaircraft use. The requirement (see 
Section 1.1) was that the fuze detonate the 
rocket in the vicinity of an aircraft target 
and within the lethal range of the rocket’s 
fragments. Although the rocket’s fragmenta- 
tion pattern was unknown, it was assumed on 
the basis of anticipated performance of the 
rocket that the region of greatest fragmenta- 


tion density would be between 60 and 70 de- 
grees off the forward axis of the rocket (see 
Section 1.3). It was next decided on the basis 
of knowledge of the radiation patterns of lin- 
ear antennas and of experimental investigations 
(see Section 2.8) that by using the rocket as 
an antenna, proper directional sensitivity could 
be obtained. 

Size and Location. Various methods of ex- 
citing the rocket as an antenna were investi- 
gated, but it was readily appreciated that the 
optimum location of the fuze from mechanical 
and service viewpoints was the nose of the 
rocket. Hence methods of exciting the rocket 
from the end were developed (see Section 2.7) 
which would give proper loading for the oscil- 
lator and the desired directional sensitivity. 
When it was established that a nose location 
for the fuze was compatible with electric de- 
sign, dimensions for the fuze were worked out. 
Since the rocket was also under development at 
the same time, it was relatively easy to coor- 
dinate the fuze requirements with rocket de- 
sign. However, space limitations were very im- 
portant, since the larger the fuze, the less high 
explosive the rocket warhead would carry. 
Enough exploratory work on circuits had been 
done at Division 4’s central laboratory at the 
National Bureau of Standards with hearing- 
aid type tubes to establish minimum space re- 
quirements for the working part of the fuze. 
Also, the National Carbon Company had devel- 
oped a small dry battery in connection with 
Section T’s shell fuze program which was suit- 
able for use as a power supply. It was agreed 
that the T-5 fuze would occupy the following 
volume: (1) a cylinder 2% in. in diameter and 
514 in. long, interior to the warhead, plus (2) 
a cone of the same diameter and 2% in. long 
exterior to the warhead and conforming to the 
contour of the ogive of the rocket. (See Figure 
1 of Chapter 5.) It was essential that the 
fuze have some external volume in order to 
provide proper excitation of the rocket (cf. 
Section 2.7) . 

Choice of R-F Parameters. (1) Carrier fre- 
quency. The miniature triodes which had been 
developed (see Section 3.1.4) worked fairly 
well in simple oscillator circuits at various 
frequencies up to about 200 megacycles. It was 


SECRET 


COORDINATION OF ELECTRIC DESIGN 


159 


desired to select a range of operating frequen- 
cies below this value at which the missile would 
be approximately resonant and also which 
would give the proper directional sensitivity 
(see Sections 2.7 and 2.9 for theoretical dis- 
cussion and Figure 33 of Chapter 5 for radi- 
ation pattern on the M-8 rocket). A range of 
operating frequencies was desired in order to 
increase the difficulty of jamming. It was also 
realized that if a range of operating frequen- 
cies was allowed, the production problem might 
be simplified. (Actually, as is shown in Chap- 
ter 6, it was found practicable to build oscilla- 
tors for fuzes with remarkably small spreads 
in carrier frequency.) 

Accordingly, three design centers for carrier 
frequency were selected, and named, for secu- 
rity purposes, Red, Yellow, and Green (see 
Glossary) . All of these were near enough to the 
resonant frequency of the missile to give suit- 
able loading and also to give suitable directional 
sensitivity. 

2. Oscillator and detector. One of the most 
direct methods of fulfilling the requirement 
(cf. Section 1.1) that the fuze be resistant to 
countermeasures is to radiate lots of power. 
Accordingly, as shown in Section 3.1.1, an os- 
cillator circuit was selected which would give 
stable oscillation under full power. (The radi- 
ated power ranged from 100 to 200 mw.) A 
sharply tuned diode detector connected to the 
antenna-coupling circuit gave suitable indica- 
tion of proximity to a target (Section 3.1.2). 
Since the fuze was intended for use on single 
missiles, the tuning of the detector introduced 
no serious problems. 

Fly-over tests and pole tests (see Sections 
2.11 and 2.12) provided basic data on the mag- 
nitude of signals which could be expected in 
the detector circuit due to approach to a target. 
In order to trigger a thyratron at distances of 
50 to 100 ft from an aircraft target, it was 
evident that appreciable amplification of the 
signal was necessary. 

Designation of Amplifier Requirements. The 
amplifier characteristics selected were such that 
a single amplifier design could be used with all 
three of the carrier frequencies selected. 

The factors involved in designing the ampli- 
fier characteristic to assist in control of the 


burst surface have been discussed in Section 3.2. 
As shown there, the gain-frequency curve of 
the amplifier was also shaped to reject certain 
undesirable signals such as vacuum-tube micro- 
phonics. The requirements for overall gain were 
determined by the magnitude of the input sig- 
nal and of the output required for reliable op- 
eration of the thyratron. As indicated in Sec- 
tion 3.3, the spread in critical bias voltage for 
thyratrons averaged about 0.4 v. To insure reli- 
able operation, a firing signal of about ten times 
the average spread value was desired. Accord- 
ingly, a bias was selected so that a firing signal 
of approximately 4 v was required. Under these 
conditions, a single-stage amplifier was able to 
provide sufficient amplification to cause opera- 
tion of the fuze at distances between 50 and 
100 ft from an aircraft target. 

Power Supply. The urgency of the request 
for an antiaircraft rocket fuze was such that 
there was no time to develop an ideal power 
supply. Accordingly the small dry battery de- 
veloped by the National Carbon Company was 
adopted for the T-5 fuze, although its limita- 
tions with regard to low-temperature operation 
and shelf life (see Section 3.4.3) were fully 
appreciated. Coordination of vacuum tube and 
battery design yielded a 1.5-v A supply and 
135-v B supply. The tubes and circuits were 
further designed so that satisfactory operation 
would continue as the A and B voltages dropped 
to values of about 1.1 and 100, respectively. 
This provision extended considerably the use- 
ful range of the batteries. 

It was realized that the high internal imped- 
ance of the miniature B battery might make 
the firing of the detonator through the thyra- 
tron a marginal proposition so a detonator 
firing capacitor was added to the power supply 
(see Section 3.3.3). With this arrangement, 
firing of the detonator was certain as long as 
the B voltage did not drop below 100 v. 

Since dry batteries deteriorate in storage, 
the fuze was designed to allow testing of the 
batteries (and also the fuze) prior to assembly 
in the field (see Section 7.7). 

Arming. Initial requirements were to have 
the fuze arm about 0.4 sec after launching of 
the rocket. To allow stable operation of the fuze 
at arming, the tube filaments and circuit con- 


SECRET 


160 


ELECTRONIC CONTROL SYSTEMS 


stants were chosen so that all warmup tran- 
sients of firing magnitude were over in about 
0.2 sec. To give the circuits maximum oppor- 
tunity for warmup, the arming switch was 
arranged to close the filament circuits during 
setback of the rocket (see Section 4.3.1). Later 
the arming was delayed first to 0.7 sec and then 
to about 1 sec, but the rapid warmup features 
of the circuits were retained. 

Mechanical Stability. Since a radio proximity 
fuze functions when a signal of requisite ampli- 
tude reaches the thyratron grid, it was impor- 
tant to prevent the generation of spurious sig- 
nals which would result in malfunction of the 
fuze (see Sections 3.1.5 and 3.2.6). Although 
proper amplifier design noticeably reduced 
some spurious signals, it was more effective 
to develop tubes and circuits which would not 
generate spurious signals or respond to in- 
duced vibration. The results of this develop- 
ment have been covered in Sections 3.1 and 3.2. 

The fuzes were subjected to intense vibra- 
tion in flight due to air turbulence produced by 
the missile and also due to vibration of the fin 
structure of the missile. In very early experi- 
mental fuzes, efforts were made to shock-mount 
the fuze to prevent these vibrations from reach- 
ing the tubes. This procedure proved unsatis- 
factory, and in all final models the tubes and 
other components were firmly embedded in po- 
sition as a solid part of a single fuze assembly. 
Embedding was accomplished with cements and 
potting compounds (see Section 4.7) which had 
the added advantage of preventing penetrat- 
ing moisture from altering the electric charac- 
teristics of the circuit. 

There remained the problem of spurious sig- 
nals generated in the missile itself. Loose fins 
on the rocket could produce variable electric 
contacts and consequently variations in the 
impedance of the rocket antenna, which would 
trigger the fuze (see Section 9.2.2). Afterburn- 
ing of the rocket powder produced trails of 
ionized gas behind the rocket, which trigger the 
fuze (Section 9.2.2 and also 2.13). Reduction 
of these difficulties was accomplished by rede- 
sign of the rocket in cooperation with repre- 
sentatives of the Ordnance Department and 
Division 3, NDRC. 

Coordination of Development Groups. Nu- 


merous laboratories worked on various phases 
of the T-5 development for Division 4. Their 
efforts were coordinated in the division office 
with the assistance of the division’s central lab- 
oratory at the National Bureau of Standards. 
In designing the fuze for production, one manu- 
facturer handled the container for the fuze, 
one the arming switch, one the battery, and five 
worked on the electronic unit. Since each of the 
latter had facilities which were best adapted to 
certain types of construction, the need for im- 
mediate production overbalanced the desire for 
production uniformity, and some three differ- 
ent structural designs were worked out. Each 
company was allowed to use that design which 
was best suited to its facilities. However, all 
companies were required to hold to the same 
performance specifications and to hold essen- 
tially the same overall dimensions. The differ- 
ence of design did not result in any material 
difference in field performance; the production 
of all manufacturers gave a relatively high level 
of performance in proof tests (see Section 
9.2.3). 


3 '°' 3 Generator-Powered Bomb Fuzes 
Ring Type 

A request for an air-to-air bomb fuze was 
made near the end of the T-5 program. This 
application meant that a longitudinal antenna 
was essential (cf. Sections 1.3 and 2.8). Prog- 
ress on the development of a wind-driven gen- 
erator had advanced to the stage where it ap- 
peared practicable to use it for the power 
supply. It appeared expedient to use the same 
type of circuits and general layout which had 
proven practicable on the T-5 project. 

An essential difference between the require- 
ment for the bomb fuzes and the T-5 fuze was 
that bomb fuzes were to be used on a variety of 
missiles of sizes from 100 to 10,000 lb. 

After development was fairly well advanced, 
the requirement was changed to an air-to- 
ground application. In order to take advantage 
of the work which had already been done, it 
was demonstrated that the amplifier alone could 
be redesigned to give acceptable air-to-ground 
performance. As a parallel but lower-priority 


COORDINATION OF ELECTRIC DESIGN 


161 


project, work was started on a transverse an- 
tenna (bar-type) fuze (Section 3.5.4). The fol- 
lowing discussion refers only to the air-to- 
ground application. 

Size and Location. The bomb fuzes were in- 
tended for use on existing missiles so the fuze 
was dimensioned to fit into standard fuze wells. 
Since most bombs were designed to carry nose 
and tail fuzes, there was a choice as to location 
for the proximity fuze. As shown in Figures 21 
to 24, Chapter 2, the radio sensitivity with an 
end-fed antenna is greatest away from the ex- 
citing end. Therefore, a tail location for the 
fuze would give greater sensitivity. However, 
proximity of the fuze and its antenna to the 
fin structure, which was known to vibrate in- 
tensively during flight, led to the conviction 
that such a location would produce malfunc- 
tioning of the fuze. 

Another consideration was that of the length 
of the fuze beyond the bomb. The fuze antenna 
must be spaced and insulated external to the 
missile in order to properly excite it as an an- 
tenna (see Section 2.7). Because of the pos- 
sible shielding effect of the fins (see diagrams 
in Figure 16, Chapter 2), a greater extension 
was required for a tail fuze than for a nose 
fuze. Furthermore, the required extension 
would make the overall length of a tail fuze 
(since it would be anchored to the bomb in the 
rear fuze well) several times greater than a 
nose fuze. The great length would make it 
much more susceptible to vibration. 

These considerations led to selection of the 
nose location for the most intensive develop- 
ment. Nose-mounted bomb fuzes with longitu- 
dinal antennas were generally referred to as 
T-50 type or ring type (see Figure 5, Chap- 
ter 1). 

Dimensions of the nose-mounted fuze exter- 
nal to the fuze well were fixed as follows. A sur- 
vey of clearances in the bomb bays of various 
bomber aircraft led to the conclusion that ex- 
tensions of more than 5 in. beyond the nose of 
the bomb would lead to difficulties in stowing 
fuzed bombs. Accordingly, the length of the 
fuze external to the bomb was required to be 
less than 5 in. The external radial dimension 
was relatively unimportant. However, a di- 
ameter of 3 1/2 in. (approximately) was found 


adequate to hold the fuze and was adopted as 
standard. 

Ballistic tests showed that the size and shape 
adopted for the fuze did not appreciably change 
a bomb’s flight. Thus, the VT-fuzed bombs 
could be used with standard bombing tables. 

Some work on lower priority was done on tail 
fuzes. There was a requirement for air-burst 
fuzes for large blast bombs (4,000- and 10,000- 
lb) . For this application there was difficulty in 
exciting the missile with a nose fuze and it was 
planned to build a special antenna system, as 
part of the fuze, in the large tail structure. 
Considerable work was done, but the project 
(fuzes T-40 and T-43) 199 was curtailed on the 
basis of incomplete reports that there was no 
advantage in air-bursting blast bombs (see 
Section 9.4.5). When the advantages of air- 
burst blast bombs were finally established, the 
T-51 fuze development was well enough ad- 
vanced for considered use on the big bombs. 

Another tail fuze project was for a 90-lb 
fragmentation bomb. In this application it was 
planned to use a special nonconducting fin on 
the bomb. Details of the work which was still in 
progress at the end of World War II are given 
in reference 196 of Chapter 2. One major ad- 
vantage of a tail-mounted fuze on an air-burst 
fragmentation bomb is the increased lethality 
of the weapon. In most bombs, the greatest den- 
sity of fragments is away from the point of 
detonation (cf. Figure IB, Chapter 1) and nose 
initiation of the explosion is therefore desir- 
able for air-burst bombs. Various schemes were 
tried for obtaining tail initiation for bombs 
when used with the nose-mounted proximity 
fuzes. 

Choice of R-F Parameters. (1) Carrier fre- 
quency. The requirement that the fuze operate 
on more than one bomb presented a problem 
in the selection of an oscillator frequency. As 
has been shown in Chapter 2, both the direc- 
tivity pattern and the radiation resistance 
change appreciably with bomb size. There was 
no singly practicable frequency (at the time) 
which would be satisfactory on all the bombs. 
A very low frequency (wavelength long com- 
pared to the bomb’s length) would give reason- 
ably uniform performance on a variety of 
bombs, but the radiation resistance would be 


162 


ELECTRONIC CONTROL SYSTEMS 


intolerably high. Circuit techniques and r-f in- 
sulating materials available at the time led to 
the conclusion that radiation resistances in ex- 
cess of 30,000 ohms would be impracticable, 
due to loss in sensitivity. 

The compromise solution was the selection of 
two frequencies, one for the 500- and 1,000-lb 
bombs and one for 100- and 260-lb fragmenta- 
tion bombs and the 2,000-lb bombs. The fact 
that the latter bomb was about twice the length 
of the 100- and 260-lb bombs made a single fre- 
quency for those bombs practicable. (See Figure 
16 of Chapter 2 for drawings of bombs.) The 
frequencies selected were designated as White 
(see Glossary in Appendix 1) for the first appli- 
cation above and Brown for the second. The first 
production models of the fuzes were designated 
as T-50-E4 and T-50-E1, respectively. Although 
the details of the argument leading to the selec- 
tion of these frequencies are too lengthy to give 
here (see reference 8 of Chapter 2) the basic 
data on which the argument was based are in- 
cluded in figures in Sections 2.7 and 2.8. 

Toward the end of World War II, circuit de- 
velopment had advanced to the stage where ade- 
quate r-f sensitivity could be obtained at higher 
radiation resistances. 118 It was then shown that 
a single frequency designated as “Brown minus 
20” would be practicable for the bomb sizes 
100- to 2,000-lb, inclusive. 140 

2. Choice of circuit. The oscillator-diode cir- 
cuit used in the T-5 fuzes was selected for use 
in the first T-50 fuzes. Tuning of the diode 
circuit presented some problem, since each fuze 
was intended for use on more than one missile 
and tuning could be optimum on only one. The 
methods of resolving the tuning compromise 
are discussed in reference 31 of Chapter 2 and 
the selected procedures for tuning are listed in 
Section 7.2. 

3. Antenna design. The evolution of the an- 
tenna cap for T-50 type fuzes is discussed in 
Chapter 4 from the mechanical point of view. 
Electrically it was desired to have a large cap 
to reduce radiation resistance (see Section 2.7). 
The forward extension of the antenna was 
limited by overall length consideration and the 
rearward extension by undesirable shunting 
capacitance on the radiating load. Another 
factor was the presence of the rotating wind- 


mill; it was desirable that it be located in a 
near-zero radio field. Compromises between the 
various factors led to a ring shape for the an- 
tenna of about 1-in. length and big enough in 
diameter to enclose the windmill (see Figures 
16 and 18 of Chapter 4). The latter figure 
shows the antenna in an earlier and less satis- 
factory form. 

Amplifier Requirements. As shown in detail 
in Section 3.3, the gain-frequency characteris- 
tic of the amplifier was adjusted to compensate 
for the variations in r-f sensitivity for various 
terminal ballistic conditions. Here, too, a com- 
promise characteristic was required because of 
different r-f properties of the missiles. 

The use of a generator power supply intro- 
duced additional requirements on the ampli- 
fier : 

1. A very sharp reduction in gain above the 
pass band was necessary in order to reduce the 
response to hum and ripple from the generator. 
In addition, hum injection circuits were em- 
ployed to reduce the net effect of hum at the 
thyratron grid. These were incorporated in the 
feedback network of the amplifier. 

2. The generator power supply made it pos- 
sible to obtain fuze operation at very low tem- 
peratures (—40 degrees) as was desired by the 
Services. Accordingly, the components of the 
amplifier had to be selected with due regard to 
their temperature coefficients in order that the 
amplifier would perform properly over a wide 
range of temperatures. 

3. Although voltage regulation circuits were 
employed as part of the power supply, they 
were not perfect and variation in supply volt- 
age was inevitable. Thus, the amplifier design 
had to be arranged so that the essential gain 
characteristics would persist over a range of 
supply-voltage variations. 

4. An average effective holding bias of about 
4 v was selected for the thyratron as for the 
T-5 fuze. However, considerations leading to 
this selection were appreciably different in the 
case of generator-powered fuzes. The variable 
contributions of hum and microphonics pro- 
duced a range of effective critical voltages (de- 
fined in Section 3.3), of about 1 v. This was 
appreciably larger than the range of critical 
biases for the T-5 fuze. Also, the method for 


SECRET 


COORDINATION OF ELECTRIC DESIGN 


163 


obtaining C biasing voltages yielded a spread 
of bias values of about 1 v. Thus the average 
effective holding bias was only about twice the 
range of variations. Although a larger margin 
might have been desirable, the requirements 
for sensitivity were such that the margin was 
made as small as was compatible with good field 
performance. 

Power Supply. The various design considera- 
tions leading to the development of a wind- 
driven generator for the power supply have 
been adequately covered in Section 3.4.5. Fac- 
tors relating to certain compromises in design 
are as follows: 

1. A supply. The supply for the tube fila- 
ments was raw alternating current at 1.4 v. 
Rectifiers or commutators to supply direct cur- 
rent would have been unduly complicated and 
it was simpler to design the circuit to operate 
with alternating current on the filaments. 

2. B supply. Plate power was rectified and 
filtered and supplied at about 140-v average 
value. Rectification and filtering were essential 
for the proper operation of the types of circuits 
employed. Some saving in space was effected by 
using the detonator firing capacitor also as a 
filter capacitor. 

The rectifier was the critical element in the 
power supply as regards low-temperature oper- 
ation of the fuze. Although it performed sat- 
isfactorily down to —40 C, requirements for 
still lower temperature would necessitate rede- 
sign of the rectifier. Some special circuits were 
investigated for operation on raw alternating 
current, but none gave completely satisfactory 
performance. 

3. C supply. Circuits were designed to obtain 
grid-bias voltage from the B supply rather than 
require a separate output from the generator. 
One advantage of this arrangement was in 
self-compensation. Overall sensitivity tended 
to remain constant as the B-supply voltage 
varied. 

4. Electric frequency. It was imperative that 
the frequencies delivered by the power supply 
be outside the amplifier pass band. Accordingly, 
the number of poles in the generator and its 
range of operating speeds were selected to give 
a minimum frequency of about 750 c under 
operation conditions. 


5. Regulation. To compensate for the fact 
that the wind-driven turbine for the generator 
must operate over a wide range of missile 
speeds (about 300 to 1,000 fps), regulation of 
the output was essential in order that circuit 
characteristics remain essentially constant. 
Regulation circuits developed (see Section 
3.4.5) kept the A and B voltages constant over 
the operating speed range within about ±5 per 
cent. Also, total voltage changes over the tem- 
perature range —40 to +60 C were less than 
10 per cent. These changes were compatible 
with good performance of the oscillator and 
amplifier. 

6. Mechanical stability. Perhaps the most 
serious problem introduced by the generator 
power supply was that of vibration caused by 
slight unbalance in the rotating system. This 
vibration tended to produce microphonics, par- 
ticularly in the triode. Solutions were sought in 
two directions; nonmicrophonic tubes and cir- 
cuits, and better balanced rotating systems. 
The work done on the two aspects of the prob- 
lem is covered in Section 3.1.4 and in Chapter 4, 
respectively. No hard and fast rules or division 
of responsibility could be set for the two prob- 
lems; they had to go hand in hand. The tubes 
had to be good enough microphonically to oper- 
ate reliably under vibration from the generator, 
and the rotating system had to be sufficiently 
well balanced that it would not produce micro- 
phonics in the tubes. There was some indica- 
tion that as balancing techniques improved, the 
generator vibration became small or negligible 
compared to that produced by the bomb in 
flight. 

The vibration problem resulted in one gen- 
eral design criterion, namely, the rotational 
frequency of the generator should be outside 
the amplifier pass band. This was a more seri- 
ous limitation on the selected range of operat- 
ing speeds than the one mentioned above con- 
cerning the electric frequency of the generator 
output. (Electric frequency was usually three 
times rotational frequency.) An upper limit on 
rotational speeds was set by the durability of 
the bearings and the centrifugal strength of the 
Alnico rotors. In some later fuze designs, nota- 
bly T-51, rotational frequency was on the upper 
edge of the amplifier pass band at arming. 


SECRET 


164 


ELECTRONIC CONTROL SYSTEMS 


Arming. The arming problems in generator- 
powered fuzes were largely mechanical and are 
discussed in Chapter 4. The requirements for 
warmup were less critical than those solved 
for T-5 fuzes. In some designs there was indi- 
cation that firing pulses would be produced at 
arming, i.e., when the electric detonator was 
connected to the circuit. Either proper circuit 
layout, by-passing or choking, was adequate to 
eliminate this difficulty. 

In rocket and mortar fuze applications, 
added RC arming was used. As shown in Sec- 
tion 3.3.6, there was an inherent spread in arm- 
ing times by this method unless considerable 
care was taken in selecting component values. 

Overall Stability. The same standards for 
rigid assembly used in T-5 fuses were extended 
and carried into the design of generator-pow- 
ered fuzes. The problems were, of course, more 
difficult because of the high rotational speed of 
the power supply system. The special layout 
chosen for the fuze was probably the most dif- 
ficult from a stability standpoint, but it had 
other advantages, as follows : 

1. Circuit arrangements, previously devel- 
oped, were used directly with only a minor 
modification to allow the generator drive shaft 
to pass down through the axis. However, it 
proved desirable to shield the drive shaft when 
it passed through the amplifier and oscillator 
block. 

2. With the windmill on the nose of the fuze, 
the aerodynamic problems were simplified. 
Later models located the entire power supply 
in the front end of the fuze, dispensing with 
the long, high-speed drive shaft (T-132) ; 
others located the generator and turbine at the 
base of the fuze using a central air duct for 
directing air to the turbine (T-82, T-172). The 
latter arrangement introduced difficulties in 
circuit layout and space requirements due to 
the central air duct. 

Difficulties experienced with T-5 and the 
extra vibration with the new power supply led 
to the elimination of all plug-in connections on 
T-50 type fuzes. The electric connections be- 
tween the various subassemblies were soldered, 
and during the various laboratory tests, sol- 
dered connecting leads were used. Although this 
increased the labor involved in making tests, it 


insured that vibrating electric contacts within 
the fuze would not introduce spurious signals. 

Spurious noise signals from the missile were 
another matter for consideration. Special wash- 
ers were used to insure both good electric and 
mechanically stable contact between the fuze 
and bomb (see Chapter 4). Service instructions 
advised that both the fuze and fin be firmly 
secured to the bomb. Reasonably careful 
wrench-tightening usually proved adequate for 
good fuze performance. However, late in World 
War II a new washer was produced which gave 
excellent results with just hand-tightening of 
the fuze (see Section 9.4.3). Occasional diffi- 
culty was encountered with bomb fins (particu- 
larly T-92 on M-64 bombs) which could be 
eliminated only by unusual precautions (see 
Section 9.4.3). In such cases, alternative fuze 
designs were sought (see Section 1.5) since 
redesign of the bomb’s fin structure was be- 
lieved impracticable. 

Coordination of Development Group. In gen- 
eral, the arrangements for coordinating devel- 
opment and experimental production followed 
the same procedure as for the T-5. Standardiza- 
tion was insisted on only when necessary, and 
considerable individuality was allowed in de- 
sign detail in order to make maximum use of 
available facilities. Various types of oscillator, 
amplifier, and generator construction are de- 
scribed in Chapter 6. 


3 5 4 Generator-Powered Bomb Fuze, 

Bar Type (T-51) 

The T-51 bar type bomb fuze was developed 
specifically for air-to-ground application. A 
transversely excited antenna was part of the 
fuze and led to the name bar type. An under- 
lying design consideration was to make maxi- 
mum possible use of T-50 mechanical parts in 
order to expedite both development and pro- 
duction problems. Accordingly, the T-51 fuze 
was mechanically identical to T-50 fuzes except 
that a nose piece with transverse bars attached 
replaced the ring-carrying nose piece. 

Size and Shape of Antenna. The overall 
length of the antenna was limited by the dimen- 
sions of the smallest bomb on which the fuze 


COORDINATION OF ELECTRIC DESIGN 


165 


was to be used. A maximum 10-in. tip-to-tip 
length was imposed. (This was approximately 
the diagonal width of the fins for M-30 and 
M-81 bombs.) As long a length as possible (up 
to one-half wavelength) was desired in order to 
reduce radiation resistance and increase sensi- 
tivity. 

Early experimental models of transversely 
excited fuzes had used screw-in dipoles, but 
considerable difficulty was encountered with vi- 
bration and variable electric contact. Accord- 
ingly, it was decided that greatest stability 
would be obtained with dipoles molded firmly 
into the nose piece. High-strength and low-loss 
dielectrics were desired and details of this in- 
vestigation are given in Section 4.7. 

Preliminary calculation indicated that the 
only suitable cross section for the antenna with 
adequate rigidity would be an airfoil section. 
Cylindrical cross sections would have given in- 
creased drag. The design chosen gave negligible 
drag in tests on 250-lb bombs. The dimensions 
of the section were selected as a compromise 
between rigidity and shunting capacity on the 
radiating load. 

Electric Parameters. The first guess in choos- 
ing an oscillator frequency for T-51 fuzes was 
that the higher the frequency up to a value 
corresponding to a wavelength equal to twice 
the antenna length (suitable tube characteris- 
tics assumed) , the better would be the perform- 
ance. Actually, it turned out, owing to unavoid- 
able electric unbalance of the antenna, that at 
higher frequencies the bombs became strongly 
resonant, and longitudinal excitation masked 
the transverse excitation. Consequently, an 
upper frequency limit was set at which bomb 
resonance would not be troublesome. A lower 
frequency limit was set by the allowable radia- 
tion resistance, below which circuit losses were 
intolerable. Designs centered around Yellow 
(see Glossary in Appendix 1) but a fairly wide 
range (10 megacycles or so) was permissible. 

Oscillating-detector circuits (RGD) were de- 
veloped to give good sensitivity under stable 
oscillating conditions (see Section 3.1). No 
tuning of the circuit was necessary and the 
fuze was usable on a wide variety of missile 
sizes (see Section 9.4.4). 

The factors leading to the selection of ampli- 


fier characteristics are adequately treated in 
Section 3.2. 

35,5 Generator-Powered Trench-Mortar 
Shell Fuzes 

The last Service requirement for VT fuzes 
was for the 81-mm trench mortar for ground-to- 
ground use. This project required a major re- 
design of the fuze, since the effect of the fuze 
on ballistics of the round was one of paramount 
importance. Some of the mortar rounds weigh 
about 8 lb, and the addition of a 2-lb fuze would 
reduce the round velocity in about the ratio of 
the increased weight. A fuze such as those used 
on bombs and rockets would completely over- 
balance the round, and even if it were satisfac- 
tory from a range standpoint, the round would 
be unstable in flight. It was therefore necessary 
to reduce the volume of the fuze by a factor of 
about 3. An additional requirement was intro- 
duced by the necessity of withstanding acceler- 
ations up to 10,000#, which was about 100 
times greater than that which rocket fuzes were 
required to withstand. Fortunately, the re- 
quirements for reduced size and increased rug- 
gedness were compatible. Two types of fuzes 
were engineered for production because of lack 
of time to work out compromises and an opti- 
mum single design. One of these used a 2 V 2 -im 
transverse loop antenna (T-172) and the other 
used the missile for an antenna. Both used 
essentially the same fuze circuits, the difference 
being similar to that between the transversely 
excited and the longitudinally excited bomb 
fuzes. 

These fuzes were the first which were engi- 
neered without much structural design rela- 
tionship to previous fuzes. They did, however, 
use the same type of components, there being 
only a minor modification of the generator and 
the rectifier assembly (see Chapter 4). There 
was, however, considerable crowding together 
and the clear-cut shielded separations between 
radio frequency, audio frequency, and power 
supply, adhered to closely in previous designs, 
were not followed. In the longitudinally ex- 
cited fuzes, the antenna cap was appreciably 
elongated to decrease the radiation resistance, 
already high because of the short missile. In 


SECRET 


166 


ELECTRONIC CONTROL SYSTEMS 


order that the space would not be wasted, the 
electric assembly, including power supply, was 
located within the antenna (see Figure 42, of 
Chapter 4). 

The longitudinal fuzes were built to two de- 
signs which were externally similar but which 
use radically different internal construction. 
One of these (T-132) represented the first ap- 
plication of a printed circuit technique (see 
Chapter 6) in which resistors and their con- 
necting wires were printed directly on ceramic 
plates with appropriate points of plating for 
the attachment of tubes, small ceramic and 
paper condensers, and for the connection to the 
power supply and detonator. The aim of this 
printed circuit development was threefold: (1) 
reduction in size through the elimination of the 
bulk of individual components such as commer- 


cial resistors, (2) increase in production speed, 
and (3) reduction of cost. This fuze was near- 
est to production status (of the mortar fuzes) 
at the close of World War II. 

The second version of the longitudinally ex- 
cited fuze (T-171) utilized essentially the same 
circuit system but different types of compo- 
nents. It was felt that the printed circuit tech- 
nique was something of a gamble, since it rep- 
resented not only a development of the tech- 
nique but of the fuze as well. For this reason, 
it was deemed necessary to engineer a similar 
fuze but using standard components whose per- 
formance was well established. Further details 
of the mortar shell fuzes, on which some design 
compromises were still in progress at the end 
of World War II, are given in Sections 3.1, 3.2, 
and Chapters 4 and 5. 


Chapter 4 

MECHANICAL DESIGN 


41 GENERAL REQUIREMENTS 

Introduction 

I N discussing the various aspects of the me- 
chanical design and construction of prox- 
imity fuzes, two approaches are possible. One 
is to treat the problems from an abstract point 
of view and to show how the final solutions fol- 
lowed inevitably the theoretical considerations 
involved. The second approach is to give the 
history of the mechanical development of the 
fuzes described in this report and to show how 
each fuze was the successor to its predecessors 
and how the considerations of expediency de- 
termined its details. 

It has been mentioned in the introductory 
chapter that time and the availability of ma- 
terials and tools were a controlling factor in 
most of the engineering designs. This was par- 
ticularly important in the mechanical design 
of proximity fuzes and consequently the history 
of the development is intimately related to all 
the mechanical designs. It would have been 
very pleasant for the designers if, at the be- 
ginning of the development of each fuze, they 
were given carte blanche in respect to the de- 
sign of the fuze, its components, the vehicle, and 
even some control as to the method of its 
launching. Unfortunately, this was not the case, 
particularly in the latter part of World War II, 
when the specifications of suitable projectiles 
and the methods of their launching preceded 
the development of the proximity fuzes. 

The limitations on the availability of compo- 
nents and on the interchangeability of the 
proximity fuzes with other types made all other 
design considerations secondary. The primary 
consideration was always time. It is for these 
reasons that, after some discussion of the gen- 
eral mechanical requirements of proximity 
fuzes, the detailed treatment of each fuze will 

a This chapter, except for Section 4.7 was written by 
Jacob Rabinow of the Ordnance Development Division of 
the National Bureau of Standards. Section 4.7 was 
written by Philip J. Franklin of the same organization. 


be taken in its chronological order so that the 
reasons for the details of its construction will 
be more readily understood. 


4,1,2 Arrangement of Main Components 

Let us consider first the case of the longi- 
tudinally excited radio proximity fuze. Since 
the vehicle itself is part of the antenna system, 
it is highly desirable for the antenna insulator 
to be as near to the mid-point of the total round 
as possible. By the use of special projectiles 
such a condition could be closely approximated. 
Very early in the program both rockets and 
bombs of special construction were built and 
tested; but it soon became apparent that it 
would be far more desirable to build fuzes 
which would fit standard missiles, and the de- 
velopment of all future fuzes was conditioned 
by this decision. 

All of the radio fuzes which went into pro- 
duction during World War II were of the one- 
piece type that fitted into the fuze well at the 
nose of the projectile. As a result of this, the 
forward antenna in all cases was a small frac- 
tion of the total length of the vehicle. In the 
case of the transverse antenna fuze there were 
other limitations on the antenna size. Mainly, 
the combined length of the dipoles should not be 
over 10 in., which was less than the maximum 
diameter of the M-57 250-lb bomb and only 
slightly greater than the diameter of the M-30 
100-lb and M-81 260-lb bomb, and the effects of 
the dipoles on the fall of the bombs should not 
require modification of the bombing tables. 

The placement of the photoelectric fuze in 
the nose of the vehicle presented a very happy 
solution, since this position was the most natu- 
ral for obtaining the “forward looking” sensi- 
tivity pattern desired. In all the proximity 
fuzes, with the exception of the T-132 and the 
T-2005 which will be treated later, the general 
arrangement was as follows : The antenna and 
oscillator unit, or the photocell, were at the 
forward end of the assembly, followed immedi- 


* SECRET 


167 


168 


MECHANICAL DESIGN 


ately by the audio amplifier. The power supply, 
consisting either of a battery or the generator 
with its associated rectifier and filter, was 
mounted below the electronic assembly and 
was, in turn, followed by the arming system 
and the explosive train. 

4,1,3 Rigidity 

A prime qualitative mechanical requirement 
in the design of the fuzes was the production of 
an assembly as rigid and as quiet as possible. 
Since the proximity fuzes are, in general, ex- 
tremely sensitive (one is tempted to say deli- 
cate) devices, the problem of microphonic noise 
is perhaps the most difficult one of all to solve. 
When it is remembered that these fuzes move 
through the air at speeds up to 2,500 fps and 
contain turbines and generators rotating at 
speeds reaching 2,000 rps, a much clearer pic- 
ture can be had of the difficulties involved. 

Dynamic balancing of the high-speed rotat- 
ing elements was utilized with great success. 
Special balancing equipment, which could be 
easily and cheaply manufactured was developed 
as incidental to the fuze program. 

4,4 Size 

The second major requirement in the design 
of the fuzes concerned the limitations on size. 
The fuzes were to be, as far as possible, inter- 
changeable with existing mechanical fuzes and 
were to be adaptable to the projectile with mini- 
mum effect on its ballistic properties. In the 
case of the larger bombs, this was not particu- 
larly difficult, since the effect of the fuze on the 
flight of the bomb is relatively small. However, 
the attempt to match the ballistics of the im- 
pact fuze with a radio fuze for the 81-mm 
mortar shell was not accomplished successfully 
during World War II. The fuzes that were 
built were appreciably larger than the impact 
fuzes and resulted in the decrease in range of 
approximately 25 per cent. 

Other Requirements 

There were many other more or less second- 
ary requirements, such as complete safety in 


handling, long shelf life, ruggedness in ship- 
ment and handling, ability to withstand heat, 
cold, and the humidity of the tropics, and the 
adaptability to as many projectiles as possible. 
There were special requirements for simple 
changes of fuze characteristics in the field, such 
as changes in the arming time, the optional in- 
clusion of self-destruction [SD] of the adapta- 
tion of the fuze to air-to-ground or to air-to-air 
service. How the particular mechanical require- 
ments were met will be described separately for 
each fuze. 


I- 2 SAFETY AND ARMING 

Comparison with Other Fuzes 

A special note should be placed here about 
the general safety and arming requirements of 
the proximity fuzes. With the possible excep- 
tion of a time fuze, the proximity fuzes present 
the most difficult problems as far as safety and 
the arming characteristics are concerned. It is 
quite obvious that the very nature of a prox- 
imity fuze is such that when fully armed and 
energized it presents extreme hazard to any- 
thing in its immediate vicinity. Accordingly, 
great effort was spent in keeping the various 
fuzes inactive until safely away from their 
point of launching. It is well to point out here 
that one of the great advantages of the gen- 
erator as compared with the battery is its 
greater safety. A generator-powered fuze 
equipped with only an electric detonator is a 
very safe device when the turbine is not turn- 
ing at a high speed. 

Very early in the work the Ordnance Depart- 
ment specified that all proximity fuzes be 
equipped with powder train interrupters so 
that, if the switching and electric safeties failed 
in some manner and resulted in an explosion of 
the electric detonator, the main explosive would 
remain unaffected. This is also the principle 
followed in most of the American mechanical 
fuzes. The only notable exceptions to this rule 
are the American bomb tail fuzes, in which the 
detonators are generally in line with the main 
explosive, but the striking pin is located away 
from the primer until properly armed by a very 


SAFETY AND ARMING 


169 


rugged and simple mechanism. This emphasis 
on powder train safety is not seen in fuzes of 
other nations, particularly those of Germany. 
Both the mechanical and electric fuzes as used 
by the Germans almost invariably had the ex- 
plosive elements in line and relied for safety on 
electric or mechanical devices ahead of the ex- 
plosives. 

The main objection to an in-line detonator 
is the possibility of its going off either because 
of a violent mechanical shock or because of the 
heat resulting from fire. The advantage of such 
an arrangement is the obvious simplicity and 
compactness. 

4,22 Difference between Rotating and 
Nonrotating Projectiles 

In general, the design of a safety mechanism 
for a fuze should use the cardinal principle that 
a fuze must arm only when subjected to all the 
forces it experiences when released against the 
enemy. The more varied the nature of these ex- 
periences, the simpler is the problem of making 
the fuze safe for our own troops. As an ex- 
ample, a fuze which is fired from a rifled gun 
experiences linear and rotational accelerations 
of great magnitude, large centrifugal forces on 
all components, and the effects of high velocity 
of travel through air ; however, a bomb dropped 
from a plane experiences very little linear ac- 
celeration, practically no rotational accelera- 
tion, and experiences the impact of a much 
slower airstream. The rockets and the mortars 
are somewhere between the bomb and the ro- 
tating shell. Some of the rockets revolve, others 
do not. Some are accelerated at approximately 
10 g, others at several hundred g. The trench 
mortar shell experiences accelerations up to 
6,000# with no rotation. Beside taking advan- 
tage of all these “natural” conditions present 
in firing of the various projectiles, other arm- 
ing means may be employed. 

42,3 Possible Methods of Arming 
Manual Arming 

Manual arming is perhaps the most common. 
It generally consists of manually setting the 


arming mechanism to operate after launching 
or actually completely arming the fuze. There 
are many obvious objections to this approach, 
and it was given up early in the program of this 
division and was not employed in any of the 
fuzes which actually reached the production 
stage. Partial manual arming, such as removal 
of the safety pin in the trench-mortar fuze, was 
built into the T-132, but the later developments 
at the conclusion of World War II made even 
this manual operation unnecessary. 

It is interesting to note that in the first of 
the proximity fuzes designed by the British at 
the beginning of World War II, the powder 
train interrupter was manually armed ; that is, 
the interrupter slider was moved into position 
by means of a screw driver. If the round were 
not fired, someone had to remember to move 
the interrupter out of line. 

Use of Arming Wire 

In the case of our bomb fuzes we used the 
traditional method of releasing the windmill or 
the turbine by means of an arming wire that 
was attached to the plane. While this method 
of arming is open to very serious objections 
and was the only one that resulted in some acci- 
dents, the considerations of standardization of 
the plane equipment were such that no changes 
in this procedure could be made during World 
War II. It is possible theoretically to arm a 
bomb fuze automatically by making use of the 
fact that a fin-stabilized projectile in flight ex- 
periences a deceleration only in the direction 
of its longitudinal axis ; in practice this is diffi- 
cult because of the low value of this accelera- 
tion and because it is conceivable that a plane 
may move in a path and at velocities equiva- 
lent to those of a freely falling bomb. 

Air-Travel Devices 

To insure the arming of the bomb fuzes at a 
safe distance from the launching plane, air- 
travel devices were connected to the windmills 
(or turbines) so that a required number of 
windmill turns had to elapse before the fuze 
would be armed. Although this is very simple 
in principle, certain difficulties arose in prac- 
tice. Different operational conditions required 
different distances to arming. Dive bombing 


' SECRET 


170 


MECHANICAL DESIGN 


techniques required quick arming, while forma- 
tion flying required very large arming dis- 
tances. This difficulty was recognized early in 
the work, but the pressure of time was such 
that variable arming was not introduced into 
the fuzes, and supplementary devices were em- 
ployed for this purpose. 

One of these devices was the T-2 arming de- 
lay shown in Figure 1A. This device was fas- 


off. (See Figure IB.) A cover using a similar 
mechanism was also developed for the T-50 
series of fuzes and is shown in Figure 2. 

Effect of Air Pressure 

The effect of air pressure on the nose of the 
projectile was also considered as a possible 
source of energy for arming rocket fuzes. One 
such system was built and tested (see Figure 



Figure 1 . A, T-2 arming device in place. This delay installed on antenna ring prevents rotation of vanes. 
Dial on delay may be set in increments of air travel up to 20,000 ft. B, T-2 delay after operation. When 
arming delay operates, it is detached from ring, allowing spring-loader plunger in ring to fly out, thus 
unlocking vanes. 


tened to the bomb fuze and was set to come off 
after any desired length of air travel from 0 to 
20,000 ft. 10 The regular arming mechanism of 
the fuze remained inoperative through this 
part of the cycle and operated in its normal 
manner only after the T-2 device was thrown 


3), but was abandoned in favor of “setback” 
devices. 

Clocks and Timing Devices 

The use of clocks and timing devices in gen- 
eral was given very serious consideration, espe- 


SAFETY AND ARMING 


171 


cially since most of the ballistic tables used by 
the Air Forces in the dropping of bombs are 
not given in terms of air travel. Nevertheless, 
clocks were not used in any of the fuzes devel- 
oped up to the end of World War II because 
of the serious objection to their lack of safety. 
A clock driven by a prewound spring is inher- 
ently a dangerous device, since once started it 
goes to the completion of its arming cycle. Near 
the end of World War II the thinking in connec- 
tion with the clocks underwent a change and, 
as will be mentioned later, the trench-mortar 
fuze was being redesigned to use a 10-sec me- 
chanical delay in its arming mechanism. Also, 
several schemes were suggested in which the 
clocks would be driven by an air turbine so that 
they would not be capable of operation unless 
the fuze were subjected to an airstream of high 
velocity. 

In the case of the rocket and mortar fuzes, 
main reliance for safety was placed on the use 
of setback or inertia-operated devices that were 
developed to a high degree of perfection. This 
resulted in fuzes that were extremely safe in 
handling; in fact, of all the thousands of fuzes 
built, tested, and used, there was not a single 
malfunction due to the failure of such a safety 
mechanism. 

Acceleration Integrators 

A new principle of setback or inertia arming 
was evolved in Division 4’s central laboratory 
at the National Bureau of Standards. It con- 
sists, in essence, of the incorporation of some 
form of an acceleration integrator into the 
fuze arming mechanism. This mechanism can 
be so designed as to preclude the possibility of 
the fuze’s arming, unless it attains a desired 
velocity. This is a sharp departure from the 
previous practice of using setback devices that 
could be triggered by intense shocks of short 
duration such, for instance, as are experienced 
by a shell in landing on a hard surface when 
accidentally dropped from some considerable 
height. In rotating shells this problem has 
never been serious because centrifugal force 
can be used in conjunction with the setback 
devices in order to make the latter shockproof. 
For mechanical fuzes for the nonrotating shells 
of the mortars, the setback device is made safe 


against accidental shocks by the use of a manu- 
ally removable arming wire. Also, the large 
values of accelerations experienced by these 
shells make it relatively easy to design a fairly 



Figure 2. Alternative arming delay. This de- 
lay completely encloses nose of fuze, preventing 
air stream from reaching vanes. When it oper- 
ates, it opens and flies off fuze as shown in 
picture at right. 

safe mechanism even if the arming wire were 
not used. 

When work on rockets and fuzes for rockets 



Figure 3. Arming device actuated by air pres- 
sure. 

was begun, however, it became apparent that 
setback devices which operate at values of 10 
to 200p were extremely sensitive to accidental 



172 


MECHANICAL DESIGN 


shock. The British in one of their early setback- 
operated switches employed a spring retained 
weight that drove a flywheel through a series 
of step-up gears (see Figure 4). While this 
type of device does act as a type of accelera- 
tion integrator, it presents a real danger when 
subjected to a very large acceleration of short 
duration. Once the flywheel is started, it tends 
to drive the mechanism to completion, even 
though the acceleration ceases. 


acts as an escapement meshing with a flutter 
bar. When subjected to an accelerating force 
greater than the force of the spring, the weight 
moves toward the tail of the projectile in a 
series of short steps. The overall cycle, there- 
fore, requires an appreciable time ; if the accel- 
eration is of very short duration, either because 
of an accidental shock or incorrect burning of 
the propellant, the weight does not reach its 
extreme rear position but stops and is moved 



Figure 4. Acceleration-operated arming device. This is a British design developed for use on their 
rocket fuzes. 


To overcome these objections a series of 
arming mechanisms was devised which can be 
divided into two basic types. One is a mecha- 
nism containing a weight retained in its forward 
position in the projectile by a spring which de- 
termines the minimum value of acceleration 
necessary to operate the mechanism. The 
weight is connected to a toothed wheel, which 


back to the initial starting position by the 
spring. A typical mechanism of this type is 
illustrated in Figure 5, showing the arming 
mechanism of the T-4, b T-5, and T-6 fuzes. The 
same escapement which is used to retard the 
weight during its initial arming cycle is also 

b The T-4 photoelectric fuze is described in Division 
4, Volume 3, Summary Technical Report. 



SAFETY AND ARMING 


173 


employed later to delay the final arming of the 
fuze. This will be discussed in detail under a 
separate heading. 

The second general class of shockproof arm- 
ing mechanisms employed the action of sepa- 
rate inertia elements, each of which is retained 
by its own spring. Consider Figure 6, which 


eration must be sustained long enough for the 
weight A to reach bottom and stay there while 
weight B executes its full stroke against the 
force of its spring. The safety of this arrange- 
ment can be shown by the following example. 
Assume springs of constant force. In the case 
cited it would take a minimum drop of 133 ft 



Figure 5. Arming device for T-5 fuzes. This device operates by integrating acceleration. 


illustrates the following: A weight A which is 
free to move for 1 in. is retained in its forward 
position by a 100-g spring. Mounted in close 
proximity to this weight is another similar 
weight B with a similar 100-g spring. It can 
also move 1 in. but only after the actuation of 
a mechanism by the motion of A. This mecha- 
nism, shown schematically in the drawing, is 
designed to keep the weight B in its initial posi- 
tion until after the weight A has reached its 
lowermost position. A similar mechanism trips 
an arming device, when the weight B reaches 
its lowermost position. 

Consider what happens if the whole mecha- 
nism is subjected to an extremely large accelera- 
tion for a very short time, as when dropped on 
a very hard surface. If the drop were made 
from sufficient height, the weight A would 
stretch its spring ; but the deceleration would be 
completely over before the weight B was re- 
leased, and the mechanism would not permit 
arming. For the mechanism to arm, the decel- 


onto a very special kind of surface that would 
decelerate the mechanism at a uniform rate of 
200gr for 8 in. before the mechanism would 
permit arming. This compares to a drop of 
8.5 ft for a simple single-element device, such 
as weight A with its spring alone. 

It is, of course, obvious that more than two 
weights can be thus interlocked and the safety 
multiplied accordingly. Three weights inter- 
locked as above would require a minimum drop 
of 300 ft under similar conditions. 

A practical device using this principle is 
shown in Figure 7, illustrating two unbalanced 
sectors, each maintained in its position by a 
75 -g spring. The flanges of the sectors are so 
arranged that the left-hand element must com- 
plete a 90-degree motion before the right-hand 
element can start. This mechanism, a switch 
designed for one of the early rockets, was 
tested by dropping from 100 ft onto a large 
variety of surfaces, from concrete to soft earth, 
without arming. It operated very satisfactorily 



174 


MECHANICAL DESIGN 


when fired in rockets with an acceleration of 
over 100#. This particular device was not used 
on a large scale because its relatively short 
arming time (0.04 sec at 125#) made it danger- 
ous in case of motor blowups. A similar device 
was also designed for the T-132 mortar fuze. 
(See Figures 8 and 42.) 



Figure 6. Double-action, acceleration-integra- 
tor, arming device. 

Other types of acceleration integrators have 
also been proposed and tested. The use of dash- 
pots was tried, but because of the general diffi- 



Figure 7. Photograph of double-action arming 
device. 

culties with the sealing of liquids and with tem- 
perature effects, this type of device was not 
used. 

sb 


424 Self-Destruction 

When projectiles are fired over friendly ter- 
ritory or when, for the reasons of security, the 
number of duds reaching enemy territory must 
be kept to a minimum, SD is required. Two gen- 
eral methods of accomplishing this were em- 
ployed. One was to use an electric circuit which 
detonated the fuze several seconds beyond arm- 
ing. This method was described in Section 3.3. 



Figure 8. Arming mechanism for T-132. This 
is a double-action device. 

The second method is to use a mechanical de- 
vice which operated a contact accomplishing 
the same result. The mechanism that was used 
in a small number of T-5 switches manufac- 
tured by the Globe-Union Company consisted 
of a long coil spring which drove an escapement 
wheel for several revolutions after the comple- 
tion of arming. One end of the spring was 
fastened to the frame, while the other was 
attached to the escapement wheel. The spring 
consisted of some fifty turns. At approximately 
three turns from the fixed end there was at- 
tached to the spring a small silver-plated con- 
tact. When the escapement made ten revolu- 
tions, this contact made only a part of a revolu- 
tion, since the rotational speed of any element 

1ET 



MECHANICAL DESIGN OF PROXIMITY FUZES 


175 


of such a coil spring is proportional to its dis- 
tance from the fixed end. In this way, speed re- 
duction was obtained without the use of gears. 
A diagrammatical illustration of the mecha- 
nism is shown in Figure 9 and a photograph in 
Figure 10. In the T-2005 fuze a differential 
screw was employed to attain the same result. 
(See Figure 47.) 

4 - 2,5 Impact Detonation 

Throughout the history of the proximity fuze 
development, considerable controversy existed 
as to the desirability of including a mechanical 
impact detonating element in the fuze. Impact 


One form of impact detonation which retains 
some of the advantages of overcoming duds 
consists of providing the fuze with inertia- 
operated switches designed to close the appro- 
priate detonator circuits upon rapid decelera- 
tion of the projectile. This device is particu- 
larly useful when a large number of duds is due 
to the failure of electric components other than 
the power supply. A simple form of this device 
(for the T-6 fuze) is illustrated in Figure 11, 
where two leaf springs equipped with silver 
contacts are mounted on the forward plate of 
the switch mechanism and are arranged so as 
to provide direct connection between the deto- 




Figure 9. Diagrammatic illustration of self- 
destruction mechanism. 

detonation, however, did not become a part of 
the formal military requirements (Ordnance 
Committee Minutes) until development of mor- 
tar shell fuzes was initiated (see Section 1.1). 
The arguments for the incorporation of this 
impact element is that in case of a failure of 
some electric component the fuze would still 
detonate the charge upon collision with the 
target or with the ground. This would serve 
both to increase the effectiveness of the weapon 
and to increase security by decreasing the 
number of duds. The objections to the use of 
an impact detonator are the greater complexity 
required in the fuze and the very great danger 
present when mechanical detonators are used, 
particularly so since the dud clearance prob- 
lems encountered by our services were very 
severe. 


Figure 10. Self-destruction element for T-5 
fuze. 

nator and the battery. 7 Only 100 of these 
switches were built before the work on the 
battery fuzes was terminated. The tests per- 
formed by the Army showed excellent results, 
with the switches operating properly upon 
ground impact down to an impact angle of 15 
degrees. Such mechanisms can be made as sen- 
sitive as desired, and the only limitation is the 
drag of the projectile in flight. In the case of 
the M-8 rocket, this drag occasionally reached 
maximum values of 18#. 

4 3 MECHANICAL DESIGN OF 

PROXIMITY FUZES 

4 31 Battery Fuzes 

The first of the fuzes developed under the 
auspices of this division, for which definite 


SECRET 


176 


MECHANICAL DESIGN 


mechanical characteristics were specified by 
the services, were the battery fuzes for the M-8 
rocket. The photoelectric and the radio fuzes 
were to be made interchangeable in all external 
respects. They were to fit a 3-in. fuze well 5 in. 
deep, and the nose contour was to be a continu- 



Figure 11. Impact detonator for T-6 fuze. 


arming switches are contained in a metal hous- 
ing. The booster charge, which is a block of 
tetryl y 2 in. long and roughly 3 in. in diameter, 
is contained in an appropriate compartment in 
the fuze housing directly below the arming 
switch. 

The main features of the arming mechanism 
for this series of fuzes are as follows. The 
arming mechanism proper is energized by the 
acceleration of the rocket. This acceleration 
acts upon a small lead weight fastened to an 
escapement wheel which is retained by a 75-g 
coil spring. The motion of this wheel is con- 
trolled by a flutter bar. The arrangement can 
be seen in Figure 5. If the mechanism is acted 
on by an acceleration greater than 75 g for a 
time longer than 0.15 sec, the lead weight 
reaches a position roughly 90 degrees from its 
starting point. This permits the operation of 
a spring-driven switch that closes the A and B 
power supply contacts, also shown in Figure 5. 
Upon cessation of the acceleration, the 75-g 
spring acting on the escapement wheel reverses 
its motion and moves a powder train inter- 
rupter carrying a tetryl lead into the armed 


ation of the rocket ogive. A photograph of the 
T-5 fuze is shown as Figure 12. The T-4 photo- 
electric fuze, which is described in Volume 3 
(Division 4 STR) used the same battery, 
switch, and housing as the T-5. 

Since the battery was to be easily replace- 
able, each of the fuzes was broken down into 
three separate components: the head or elec- 
tronic assembly, the battery, and the safety and 
arming mechanism. The three parts were ar- 
ranged to be connected by plugs and sockets. 

The mechanical design of the head is rather 
simple. In the case of the radio fuze, the nose 
is made of mica-filled phenolic into which a 
small antenna cap is molded. In some of the 
fuzes this cap was spattered onto the surface 
of the phenolic. The nose is hollow and contains 
an oscillator block supported by a metal shelf 
below which are mounted the amplifier com- 
ponents. The base of this head consists of an 
insulating plate provided with pins which fit 
into corresponding socket holes in the top plate 
of the battery. The arming mechanism and 



Figure 12. T-5 fuze, components and assembly. 

From left to right: electronic assembly desig- 
nated as MC-382; battery power supply desig- 
nated as BA-75; arming switch designated as 
SW-200; housing which contains tetryl booster; 
partial assembly of fuze; fuze completely assem- 
bled ready for installation in rocket. 

position. Mounted on this interrupter bar is a 
small switch element that closes the detonator 
circuit near the end of the bar’s travel. In this 
manner the fuze is not fully armed either elec- 
trically or mechanically until long after the 
cessation of acceleration. In most of the switches 



MECHANICAL DESIGN OF PROXIMITY FUZES 


177 


built, this amounted to roughly 0.8 sec after the 
launching of the rocket. 

A note about switch contacts should be made 
at this point. In many of the switches which 
preceded the production model described above, 
the contacts were mounted on leaf springs, as 
is the common practice in many relays and tele- 
phone jacks. It was soon discovered that these 
“pressure” contacts were extremely micro- 
phonic and caused malfunction of the fuzes 
because of the resultant electric noise. The 
rotary-type of radio switch that was finally 
adopted was far better in this respect. This 
was probably due to the fact that the contact 
pressures were somewhat greater and that the 
springs were extremely short, resulting in ex- 
tremely rigid contact assemblies. Other types 
of contacts, particularly of the wedge-type, 
were also tested, but the availability of the type 
shown resulted in their exclusive use. Work on 
the engineering and the production phases of 
these arming mechanisms was done by the 
Globe Union Company of Milwaukee. Many 
variations of these switches were built by this 
company. They differed in the arming time, the 
value of acceleration for operation, the pres- 
ence of impact detonating switch elements, the 
incorporation of SD, and many variations in 
the electric circuit. 

The detonators for the fuzes were inserted 
into the arming switches through an opening 
in the top plate. This operation could be per- 
formed after the switch was completely assem- 
bled and tested. At the request of Army Ord- 
nance an additional safety feature was later 
added which consisted of a key passing through 
the top plate of the switch. (See Figure 5.) 
The key was so arranged that if the mecha- 
nism, for some reason, began its arming cycle, 
the key could not be removed. This in turn pre- 
vented the switch from being plugged into the 
battery. If the arming mechanism was in the 
correct and safe position, the key could be 
easily removed and discarded. Of the hundreds 
of thousands of switches made, tested, and 
used, no case of malfunction resulting in an 
accident was reported. 

Since the assembled fuze had to be capable 
of withstanding an acceleration of several hun- 
dred g, the components were required to pass 
a centrifuge test at l,000p. Large centrifuges 


were built for these tests by the National 
Bureau of Standards [NBS] and by the vari- 
ous contractors involved (see Figure 13). 


Generator Fuzes for Rockets 
and Bombs 

Early RRLG Fuze for Rocket Application 

As mentioned elsewhere in this report the 
shortcomings of the battery were quite obvious 
to all concerned, and, shortly after the battery 
fuzes went into production, work was started 
on the use of air-driven generators for power 
supply. Since the efforts at that time were di- 



FlGURE 13. Centrifuge for testing T-5 fuze. 


rected toward the development of a fuze for 
the M-8 rocket, the generator and its driving 
system was designed to fit into the general pat- 
tern of the T-5 fuze; there was a strong effort 
made to use as many components of that fuze 
in its successor as possible. The obvious solution 
was to mount the generator below the head, 
in the space originally occupied by the battery, 
and to drive it by means of an insulating shaft 
connected to a windmill in the nose. Such an 
arrangement is shown in the radio rocket lon- 
gitudinal generator [RRLG] fuze shown in 
Figure 14. The antenna still consisted of a 
small metal cap directly under the vane, all of 
the vanes used in these fuzes were of Bakelite. 


SECRET 



178 


MECHANICAL DESIGN 


The shaft connecting the windmill to the gen- 
erator had to be of an insulating material so 
as not to short-circuit the antenna system. 
Cloth-filled Bakelite was found most suitable 
for this purpose. 

At this time precision ball-bearings were not 
available in quantity, and in the first attempts 
to get satisfactory bearings for the high speeds 
involved, porous bronze (Oilite) bearings with 
steel shafts were used. These were acceptable 
in the generator but did not operate properly 


In connection with the RRLG the question 
arose as to whether the old plug-in arming 
system should be retained, operated only by set- 
back, or whether advantage should be taken of 
the vane action and the arming be made depend- 
ent on both acceleration and air travel. Since 
the emphasis on the safety of the proximity 
fuzes at the beginning of World War II was per- 
haps inordinately large, it was decided to aban- 
don the pure setback mechanism and to employ 
a safety device which would not arm unless 





FILTER CONDENSER 


/ 

GENERATOR COVER 


ENCASING CAN 


SQUIB ROTOR 




RF-AF SUBASSEMBLY 
POTTED 

ASSEMBLED POWER SUPPLY 
AND ARMING MECHANISM 


OSCILLATOR BLOCK AND 
SHIELD PLATE 

ft 


COMPLETE ASSEMBLY 


GENERATOR ROTOR 
SET BACK LOCK 


SAFETY PLATE TETRYL CUP 


AMPLIFIER ASSEMBLY 


RF-AF SUB ASSEMBLIES 


COMPLETE RF-AF HEAD 


T-12 (RRLG) ROCKET RADIO FUZE 
GENERATOR POWERED 


GENERATOR SET BACK RELEASE 
ARMING GEAR TRAIN RECTIFIER 
SELF DESTRUCTION 


Figure 14. T-12 fuze, complete assembly and principal components. 


as nose bearings, primarily because of the 
thrust on the windmill and the large amounts 
of unbalance present. Home-made ball-bearing 
races were utilized with success (Figure 15). 

In the rocket application, for which the first 
generator fuze was designed, the air velocities 
were limited to a rather narrow range between 
800 and 1,500 fps, and no difficulties were ex- 
perienced with excessive speeds of the gen- 
erators. This was not the case later in bomb 
fuzes. 


acted upon by both air impact and acceleration. 
The RRLG fuze, or T-12 fuze (Ordnance De- 
partment nomenclature) , was not manufactured 
on a large scale because, at approximately the 
time the design was completed, further work 
on the M-8 rocket was stopped. The general 
philosophy, however, of combining air drive 
with setback was carried over into all the later 
fuzes. Biblographical references dealing with 
this fuze are NBS reports on RRLG or T-12 and 
reports of the Rudolph Wurlitzer Company. 74 


| SECRET 


MECHANICAL DESIGN OF PROXIMITY FUZES 


179 


T-50 Bomb Fuze 

Overall Design Details. The next requirement 
for a proximity fuze was for a generator- 
operated fuze for bomb use. Since the head and 
the generator as used in the RRLG appeared 
to be satisfactory, they were incorporated into 



facturers of Alnico rotors and of the fuzes (see 
Figure 17). The rotating system of this ultra 
centrifuge is an air-supported turbine rotor 
capable of speeds in excess of 120,000 rpm. 

The original windmills had three blades of 
2-in. overall diameter ; however, when they 
were released at high altitudes and at low plane 
velocities, the rotational speeds did not repeat 
well. Therefore, the design was changed to a 
2 V 2 -im windmill that had considerably larger 
power output, resulting in more reproducible 
speed. Since the bomb velocity varied from ap- 
proximately 200 to 900 fps, the speed of the 
vane varied over a corresponding range. This 
resulted in extremely high top speeds; since 


GENERATOR PROPELLER 


Figure 15. Vane and vane bearings for gen- 
erator-powered bomb fuze. 

the T-50 series of fuzes but with some changes 
in the arming system and the overall exterior 
shape in order to adopt them to bomb use. The 
nose fuze well of most of the American bombs 
used a 2-in. thread ; therefore, an adapter case, 
which because of its general physical appear- 
ance became known as the “potato masher,” 
was designed to house the entire mechanism. 

A photograph of a cutaway of a typical T-50 
fuze is shown in Figure 16. As can be seen, 
the general arrangement is similar to that of 
the RRLG fuze in that the electronic compo- 
nents of the nose are followed by the power 
supply and the arming system. The rectifiers 
for the power supply are mounted in the Bake- 
lite housing surrounding the reduction gear, 
while the filter and firing condensers are made 
in a tubular shape and mounted in the space 
surrounding the low-speed arming shaft. The 
vanes, or windmills, originally used in the T-50 
were made of either cotton flock or rag-filled 
phenolic materials. It was found that such 
vanes could withstand rotational speeds up to 
80,000 rpm without bursting. Some of the cast 
Alnico generator rotors could not withstand 
such high speeds, and it was necessary to per- 
form a large amount of high-speed testing. An 
ultra centrifuge was developed for this purpose 
at NBS and was adopted by many of the manu- 


TRANSMITTER 

RECEIVER 


POWOER TRAIN 



GENERATOR 


FIRING UNIT 


Figure 16. 
fuze. 




Cutaway of typical T-50 type bomb 


dynamic balancing was not employed in the 
initial production of these fuzes, great difficul- 
ties arose due to the failures of bearings and 
the presence of microphonic noise. 

Several lines of attack were followed to over- 
come these difficulties. One concerned the use 
of interchangeable windmills that could be eas- 


CRET 


180 


MECHANICAL DESIGN 


ily changed in the field in order to select the 
type most suited to the plane speed and the 
bombing altitude. Another involved the bal- 
ancing of the vanes to eliminate vibration and 
thus permit the use of a single high-speed wind- 
mill for all applications. It was found that the 
interchangeable units could not be easily bal- 
anced, and this method was soon abandoned. 



Figure 17. Ultra centrifuge for testing rotors 
for T-50 type fuzes. 


One interesting by-product of the plan to use 
interchangeable turbines was the special T-50 
shipping can with a special container built into 
its cover for one or two spare units. This addi- 
tional space later proved itself very convenient 
for packaging the T-2 extended arming device 
which, in fact, was specifically designed to fit 
this package. 

Dynamic balancing will be discussed at the 
end of this chapter (see Section 4.6). 

In the first bomb fuzes the antenna still con- 
sisted of a small streamlined cap directly below 
the vanes, but for electrical reasons it was soon 
changed to a thin ring approximately 3 in. in 
diameter that was supported by four buttresses 
extending from the nose section, as seen in 
Figure 18. A short time later the ring was 
lengthened to approximately % in. (see Fig- 
ure 16) and this was the antenna that, with 
minor variations, was carried into all the later 
fuzes of this general type. (See Section 2.7.6 
for electrical reasons for increasing length of 
ring.) This longer antenna ring also performed 
several useful mechanical services. It acted as 
a guard for the vanes and at the same time pro- 
vided a convenient anchorage for the vane 
locking pins and extended arming devices. 

The enclosing of the windmill in a long an- 
tenna ring also gave rise to the possibility of 
using metal vanes. Successful tests were made, 


and shortly thereafter most of the manufac- 
turers changed to the use of stamped steel 
10-bladed windmills. Some difficulty was ex- 
perienced with metal fatigue and breakage of 
the blades, but this was rectified by the use 
of ribbing at the thin section near the root of 
each blade (see Figure 19). These windmills 
were also dynamically balanced in production. 
Until very near the end of the T-50 program 
the vane shafts were equipped with ball bear- 
ings of the type shown in Figures 15 and 18B. 
The races were machined in steel and case- 
hardened. The balls were of the quality used in 
precision bearings. Because of the absence of 
thrust and of the inherently better balance, the 
generator bearings were of the simple sleeve 
variety. The shafts were of stainless steel, while 
the bearings were of porous bronze, commer- 
cially known as Oilite. Near the end of World 



Figure 18A. Photograph of assembled T-50 
type bomb fuze. 


War II most of the manufacturers began to 
use precision ball bearings, both for the tur- 
bines and in the generators. 

In the original design of the T-50, the cou- 
pling shaft, that is, the shaft coupling the 
windmill to the generator, was loosely coupled 
at both ends. The engineers of the General 
Electric Company suggested and experimented 
with a design in which the coupling shaft was 
rigidly attached to the windmill but was loosely 
coupled only at its bottom end. This required 
only one ball bearing at the nose instead of two. 
The design was generally adopted and its use 
resulted in a simpler, more rigid, and more 
economical assembly. 17 It is shown in Figure 16. 

Experiments at Bowen 75 and at the National 
Bureau of Standards 18 showed that noise was 


MECHANICAL DESIGN OF PROXIMITY FUZES 


181 


still caused by the looseness of the coupling 
between the insulating shaft and the generator. 
Experiments were performed on the use of 
rubber and other flexible materials as vibration 
absorbers at this point. A final design was 
evolved in which the generator was driven 
through a tight-fitting rubber coupling. This 
also served to minimize the rotational oscilla- 
tions of the generator rotor that had caused 
phase modulation in the generator output. This, 
in turn, modulated the voltage output of the 


wires were employed to hold the vanes and the 
arming mechanisms in the “safe” condition 
(see Figure 20). After release, the windmills 
were required to make a definite number of 
turns to arm the fuzes. The electric arming of 
the generator fuzes was considerably simpler 
than that of the battery fuze, since no A or B 
switches were required. In the original RRLG 
rocket fuze, SD was a requisite, and the gear 
train was, therefore, arranged to continue its 
operation after the explosive train was aligned. 



Oscillator block 

Amplifier 

Generator 

Rectifier 

Filter condenser 

Contacts to detonator 

Detonator 

Tetryl plate 

Windmill 

Vane bearing assembly 
Drive shaft 


N Antenna (in later models, antenna extended forward to 
enclose vane) 

P Insulating support for antenna 
Q Fuze housing (“potato masher”) 

R Speed reducing gears 
S Lugs for wrench 

T Low-speed drive shaft for arming mechanism 
U Locking pin for detonator rotor 

W Detonator rotor (arming consists of rotation of this piece 
into proper position) 

X Booster cup 


Figure 18B. Sectionalized drawing of T-50 type bomb fuze. Same general arrangement of parts used 
for all ring-type bomb fuzes. 


power supply when the latter was operated on 
the steep part of its voltage-versus-speed regu- 
lation curve. 

Some further reduction in mechanical noise 
could have been obtained by dynamic balancing 
of the generator rotors, but because this would 
have necessitated major changes in the assem- 
bly, it was not resorted to in the T-50 and T-30 
series of fuzes. 

The Arming System. Since bombs experience 
no acceleration of large magnitude, arming 


An SD contact was arranged to close the det- 
onator circuit at the desired time after arming. 
This feature of a continually running gear 
train was carried over into the bomb fuze, 
since the possibility of converting them back 
into rocket fuzes was always present. 

From the point of view of noise and micro- 
phonics, it would have been better to design 
the gear train so that it would be disconnected 
from the vane at arming, and several methods 
of doing this were, in fact, suggested, but the 


SECRET 




182 


MECHANICAL DESIGN 


possibility of requiring SD and the availability 
of the gear train (from the RRLG program) 
together with the ever present pressure of 
time kept the mechanism as it was. The first 
gear trains used in the T-50 series of bombs 



Figure 19. Unfinished windmill for T-50 bomb 
fuze, showing flutings for increased rigidity. 

were of the planetary-differential type. A pho- 
tograph of this gear train is shown in Figure 
21. This differential gear appeared particularly 
desirable for these mass-produced fuzes be- 
cause of its simplicity and cheapness. It was 
designed originally for the RRLG rocket fuze, 
for which speeds in excess of 80,000 rpm were 
not expected, and no serious trouble with noise 
or short life was anticipated. This, however, did 
not prove to be the case in the bomb applica- 
tion. These gears suffered from several grave 
defects. One was their short life under high 
speeds of operation, and the other was the 
large amount of noise and vibration they intro- 
duced into the fuze. 3 In order to overcome these 
difficulties, a worm type of gear reduction, 
which fitted the space allotted to the differential 
gear, was designed (see Figure 22). The only 
change necessary in the fuze for its adoption 
was a change in the generator shaft, which 
now incorporated a worm at the first step of 
the gear reduction. These worm gears, which 
were engineered by the Globe Union Company 51 
and produced by them and several other con- 
tactors, were used in all of the bomb fuzes 
with excellent results. The overall reduction in 
speed from the windmill to the arming shaft 
was approximately 5,800 to 1. 

A rather radical departure from the previous 


arming systems was introduced into the method 
of interrupting the powder train. Instead of 
keeping the electric detonator in a fixed posi- 
tion and moving a slider containing one of the 
other powder train elements, it was decided 
that considerable increase in simplicity and de- 
pendability could be achieved by moving the 
electric detonator itself so as to interrupt both 
the explosive train and the electric firing cir- 
cuit. A small Bakelite drum was arranged to 
be driven by the low-speed shaft of the gear 
train. This drum carried the detonator with 



Figure 20. Use of arming wire and locking pin 
to prevent vane rotation. 


its two electric contacts and a small transfer 
pin which acted as a coupling between the drive 
shaft and the drum and also served as a lock 
for the detonator assembly when in the armed 
position. Since the gear train ran continually 
before and after arming, SD could be achieved 
by the insertion of a special washer under the 
detonator drum in order to ground the thyra- 


SECRET 


MECHANICAL DESIGN OF PROXIMITY FUZES 


183 


tron plate circuit and thus fire the detona- 
tor. 

Because of the direct relation between the 
vane speed and the velocity of air travel, the 



Figure 21. Planetary-type speed-reducing de- 
vice for T-50 fuzes. 


the tetryl lead in the safe or unarmed position. 
This limited the unarmed angle setting, called 
the arming angle, to the range of more than 
60 degrees and less than 300 degrees. Angles 
from 100 to 180 degrees were most commonly 
used in practice. 

The electric connections to the detonator were 
made through two phosphor bronze or beryl- 
lium-copper leaf springs mounted in the det- 
onator rotor housing. These silver-plated 
springs made contact to two small silver-plated 
screw heads, under which the detonator leads 
were fastened. The system of contacts described 
above had several serious faults: the springs 
could be easily deformed in handling so as to 
result in poor contact, and the transfer pin 
had to be rather carefully made because if it 
failed to snap out of the slot in the shaft and 
lock the detonator rotor into its armed position, 
the rotor would turn through the armed posi- 
tion and cause the fuze to be a dud. 

The exact length of air travel to arming 
could not be exactly preset because the manu- 
facturing tolerances in this assembly were such 
that small erorrs could cause large differences 


PROPELLER GENERATOR SLOW SPEED SHAFT SAFETY PLATE 

ROTOR 



t - ' Lw,. V <7* ; 

COUPLING SHAFT GEAR TRAIN DETONATOR ROTOR TETRYL CUP 



Figure 22. Arming mechanism of T-50 type fuzes with worm gear. 


distance through which a bomb fell before arm- 
ing was easily controllable by a change in the 
angular setting of the detonator rotor. The only 
limitation on this was the fact that the det- 
onator had to be at least 60 degrees away from 


in the arming distance. Some of the fuzes pro- 
duced near the end of the program were set by 
manual or automatic counting of windmill 
turns. This difficulty was not anticipated in the 
design because the need for precision arming 



184 


MECHANICAL DESIGN 


of the proximity fuze was not expected. It was 
thought that merely delaying the arming for 
an approximate distance would be sufficient. 
The using services, however, laid down rather 
stringent requirements during, the course of 
the development program, for the minimum 
and maximum limits of safe air travel, and 
several minor modifications in the arming sys- 
tems were introduced as a result. 

A removable safety pin similar to the key 
of the T-5 switch was added to the arming sys- 
tem of the T-50. This pin had to be manually 



Figure 23. Safety pin installed in T-50 type 
fuzes. Pin is removed before fuze is inserted in 
fuze well. 


later manufactured as the T-51 fuze by the 
Zenith Radio Corporation (see Figures 26 and 
27). 71 The final model of T-51, which carries a 
bracket for the vane locking pin, is shown in 
Figure 5 of Chapter 1. 

Several types of dipoles were experimented 
with at the National Bureau of Standards. One 
was the metal type molded into the antenna 
head, and the other consisted of plastic dipoles, 
made integral with the head, over which a con- 
ducting surface of metal was either plated or 
spattered. Metal dipoles were used by the 
Zenith Corporation in their production. 

T-82 Bomb Fuze 

A markedly different bomb fuze, the T-82, 
was developed by the Westinghouse Company. 68 



Figure 24. Details of arming safety pin de- 
vice. 


removed before the fuze could be screwed into 
the bomb well. This pin indicated that the det- 
onator rotor was in the safe position, and it 
could also be used as a later check if, for some 
reason, the fuze had to be removed from the 
bomb after a flight. The details of this safety 
system are shown in Figures 23 and 24. 

T-51 Bomb Fuze 

A modification of the T-50 fuze was made by 
changing the antenna to one of the dipole 
variety (see Figure 25). The mechanical ar- 
rangement was almost exactly identical to that 
of the T-50 except that plastic windmills were 
used to the end of production. This fuze was 


(See Figure 28.) In an effort to overcome the 
vibration difficulties encountered in the design 
of the T-50, the rotating system of this fuze 
was located in its base so that it could be nearly 
totally enclosed by the fuze well. By using a 
radial flow turbine mounted directly on the 
shaft of the generator and supporting the 
whole high-speed assembly by a metal casting 
mounted in the nose of the bomb, an extremely 
rigid and quiet mechanical design was achieved. 
The air to drive the turbine was conducted 
through the electronic components by a central 
duct and exhausted through two wide ports 
near the base of the fuze. The main body of the 
fuze was made of mica-filled phenolic and was 


MECHANICAL DESIGN OF PROXIMITY FUZES 


185 



Figure 25. Early model of T-51 fuze. 


gether by four screws. The gear reduction was 
of a worm type similar to that used in the T-50, 
and the arming system was identical. 

No dynamic balancing was employed in this 



Figure 27. Assembly and principal components 
of T-51 fuze. 


connected electrically to the power supply and 
the arming system by means of a multiple pin 
plug. These two main assemblies were held to- 


fuze, but precision ball bearings were used in 
all models. In order to limit the top speed of 
the turbine, automatic speed regulation of sev- 
eral kinds was tried, and it was found that, by 




ASSEMBLY ASSEMBLY HOUSING 


GENERATOR 

ASSEMBLY 


£ # 

ADAPTER ROTOR TETRYL PLATE 

rrrr r T“;-"'-r : !i 


Figure 28. Assembly and principal components 
of T-82 fuze. 


making the blades of the turbine of spring 
steel, they could be made to change their curva- 
ture, or pitch, when acted upon by both cen- 
trifugal force and air pressure. The production 



Figure 26. Later model of T-51 fuze. 



186 


MECHANICAL DESIGN 


model of the fuze employed four rigid and four 
flexible plates, shown in Figure 28. It was 
found in practice, however, that the range of 
speeds over which this fuze operated did not 
result in any speed regulation of this particular 
turbine, but the top speeds did not cause any 
trouble, because of the excellent bearings 
used. 


train was, therefore, developed at the National 
Bureau of Standards, which was again de- 
signed for production and produced by the 
Globe Union Company. Figure 29 shows the 
construction of this gear train, and again only 
the main features of its operation will be 
stated. For proper arming the mechanism re- 
quires a sustained acceleration of more than 



Figure 29. Arming device for T-30 and T-2004 fuzes. A, parts in their normal position; B, inertia 
element in position assumed during setback. 


Generator Rocket Fuze 
T-30 (and T-2004) 

As mentioned previously, work on the M-8 
rocket was discontinued, and emphasis was 
placed on the use of the fin-stabilized Navy 
rockets developed at the California Institute of 
Technology. It was quite apparent that with 
slight modifications the T-50 bomb fuze would 
serve excellently on these projectiles. With a 
minor change in the vane pitch, the fuze could 
have been used “as is,” but the presence of 
reasonably large values of acceleration offered 
attractive possibilities of increasing the safety 
of the arming mechanism. A new type of gear 


lOp occurring simultaneously with the rapid 
motion of the fuze through air for 300 ft. The 
windmill is locked by the usual arming wire, 
when the rocket is in its launcher. If this arm- 
ing wire were prematurely withdrawn, the 
windmill would start rotating, but due to the 
absence of acceleration the mechanism would 
jam, one of the brass gears would strip, and the 
fuze would become a dud if fired. 

The arming system was further designed so 
that the mechanical and electric arming was 
not completed until after the cessation of accel- 
eration. This was done to prevent the fuzes 
from being set off at some point beyond the 
300 ft by the burning of the propellant. The 


MECHANICAL DESIGN OF PROXIMITY FUZES 


187 


RC arming delay which followed the comple- 
tion of the mechanical arming cycle increased 
this safety still further. 

Since this gear train was so designed that the 



Figure 30. Doughnut arming device installed 
in fuze. 

low-speed shaft did not rotate after the comple- 
tion of mechanical arming, no SD was incor- 
porated into the T-30 and the T-2004 fuzes. For 
the same reason, the detonator rotors were not 
provided with a transfer pin but were perma- 
nently locked to the low-speed shaft. 

The T-30 and the T-2004 fuzes were pri- 
marily designed for stop-gap use, while the de- 
velopment of special rocket fuzes was in prog- 
ress (see Section 4.3.4 on T-2005) and the 
setback gear train was designed with this in 
mind. The major objection to the modified bomb 
fuzes as rocket fuzes was their size, which meas- 
urably increased the drag on the missile. The 
use of arming wires in rocket fuzes was consid- 


ered objectionable by NBS engineers, and the 
employment of a setback mechanism that could 
not be inspected from the outside and that re- 
sulted in a dud in case of malfunction of the 
arming wire was not considered an elegant 
solution. 

The British Air Forces requested Division 4 
to design an arming mechanism that would 
convert a T-50 into a rocket fuze but that would 
keep the vane from turning and release it only 
by the action of setback. No arming wires were 
to be required and no loose components, such as 



Figure 31. Doughnut arming device for rocket 
fuzes. A, plunger in armed position; B, plunger 
in unarmed position where it prevents rotation 
of vanes. 

pins, were to be released in flight. Accordingly, 
a “doughnut” arming mechanism was devel- 
oped. 41 This mechanism, shown in Figures 30 
and 31, fitted inside the antenna and held the 
vanes in the locked position by a small pin. A 


SECRET 


188 


MECHANICAL DESIGN 



flutter type of mechanism was enclosed in the 
ring and, when subjected to an acceleration of 
more than 10 # for more than 14 sec, caused the 
release of the vanes. The engineering and pro- 
duction of this unit was done by the Transition 
Office of NDRC and by the Solar Aircraft Com- 
pany of California. An interesting feature of 
this device is the circular flutter weight, with 
its center of gravity on the center line of the 
fuze. This made the mechanism operable in the 
presence of slow rocket spin (about 1,000 rpm, 
the spin rate of one of the British rockets for 
which the mechanism was designed). The use 
of the ring-shaped weight enabled its designers 
to obtain a large moment of inertia with a 
minimum of total mass. This device was able to 
pass the standard jolt test without difficulty. 


Figure 32. Front view of high-# centrifuge for 
testing mortar fuzes. 

4 3 4 Miniature Fuzes for Trench Mortars 
and Rockets 

Fuzes, T-132 and T-171 

When Division 4 undertook the development 
of a generator proximity fuze for trench-mor- 


tar use, completely new problems of mechanical 
design arose. The accelerations experienced by 
a mortar shell are of entirely different magni- 
tude from those to which the physicists and 
engineers were accustomed in their work on 


Figure 33. Side view of high-# centrifuge for 
testing mortar fuzes. 

bombs and rockets. An 81-mm mortar shell is 
fired from its gun with varying accelerations up 
to 6,000#. The resulting stresses obviously re- 
quired a new approach to the mechanical design 
of the proximity fuze. This point in the fuze 
program represented a welcomed opportunity 
for incorporating into the new fuze a great 
many of the suggestions and ideas which were 
gathered in the previous work. 

New testing techniques had to be developed 
for this work. Although it is practically impos- 
sible to duplicate the gun accelerations in the 
laboratory, a close approximation can be made 
by using a special centrifuge. Accordingly, 
NBS designed and built a high-# centrifuge 
capable of testing complete mortar fuzes at 
accelerations up to 15,000#. Photographs of 
this equipment are shown in Figures 32 and 



MECHANICAL DESIGN OF PROXIMITY FUZES 


189 


33. Two Dural arms, such as are used in the 
machine, can be seen in the photographs. 

The requirement for extreme compactness 
presented, besides the mechanical problems, the 
problem of securing a sufficiently large antenna 
to insure adequate r-f loading. In order to ac- 
complish this, the usual arrangement of the 
antenna and ground of the proximity fuze was 
reversed. It was decided to make the body of 
the fuze the ground, and to use the vehicle as 
the antenna. This, of course, is merely a jug- 



Figure 34. Diagram showing arrangement of 
principal components in T-132 and T-171 fuzes. 


gling of words, but it helps to explain how, for 
a fuze of a given size, a better arrangement can 
be made by locating the antenna insulator di- 
rectly ahead of the nose of the projectile and 
mounting as many of the mechanical and elec- 
tronic components of the fuze as possible ahead 
of this antenna “break.” A diagram of the 
general arrangement of the resulting fuze is 
shown in Figure 34. 

The possibility of using a base generator, as 
was done in the case of the T-82, was seriously 
considered but was discarded because of the 
considerable space occupied by the air passages. 
Accordingly, the turbine and the generator 
were mounted in the forward end of the fuze. 
The decision to do this was further strength- 
ened by the requirements that the fuze operate 
at very low airspeeds. In the case of a 0 charge, 
the 81-mm shell leaves the gun at approxi- 
mately 150 fps, making the successful opera- 
tion of the turbine difficult. More will be said 
about this matter in connection with the T-172. 


The generators used in the experimental 
trench mortar fuzes were originally identical 
with those designed by Zenith for the T-50, 
with the exception that the six corners of the 
stator were machined off, giving a circular 
stator with an outside diameter of 2 in. It was 
found that the removal of the corners did not 
reduce the output of the generators. This six- 
coil design was adopted by the Globe Union 
Company in their production of the T-132. 50 
The Wurlitzer Company, however, because of 
their experience with the wave-wound T-50 
generators decided to experiment with a double 
snake-wound generator of somewhat smaller 
size (see Figure 35). This design, when used 
with a voltage doubling rectifier circuit, proved 
quite satisfactory. 

The problem of supporting the coils and 



A B 


Figure 35. Generator stator for T-171 fuze 
(right) shown in comparison with stator for 
T-50 fuze (left). 

laminations against the force of setback was 
met by centrifugal potting of the stator, using 
a special high-temperature potting compound 
(see Section 4.7). The stator of the generator 
was enclosed in a thin metal shell, and the 
whole assembly was rotated about the central 
axis of the generator at approximately 7,000 
rpm. A measured quantity of the hot potting 
mixture was poured into the generator frame. 


SECRET \ 



190 


MECHANICAL DESIGN 


The centrifugal action forced the liquid to 
spread into the space around the coils and form 
a cylindrical inner surface just back of the 
pole faces. The material was cooled while still 
spinning at the high rate. 

The dynamic balancing of the high-speed 
rotating system eased the problem of the bear- 
ing design very greatly. Precision bearings 



Figure 36. Protective cover and arming pin for 
T-132 fuze. 

were incorporated into only a small number of 
fuzes. It was found that the New Departure 
R-3 (V 2 in. OD, % 6 ID) was capable of with- 
standing a static thrust of nearly 1,000 lb and 
then was able to operate at 100,000 rpm for 
several minutes without failure. The procure- 
ment problem was still very serious and since 
experiments indicated that sleeve bearings, 
particularly of the Oilite-type, could be em- 
ployed satisfactorily, the Globe Union Com- 
pany did considerable research on their use. 
The engineers of the Allis-Chalmers Company 
in Milwaukee urged the adoption of rubber 
mounting of the bearings, since their experi- 
ence with the high-speed rotating machinery 


indicated that some form of damping was re- 
quired for these bearings. The Globe Union 
Company adopted this suggestion, and the use 
of rubber mounting for the sleeve bearings was 
standard in all of their production of the T-132. 

In the summer of 1945 the University of 
California was asked by the Transitions Office 
of NDRC to pursue further the research on 
the bearings and rotating components for the 
mortar fuzes. This group found that shafts 
with extremely hard surfaces were suitable for 
this service. 60 The National Bureau of Stand- 
ards also conducted research in the same field 
and had excellent results with bearing assem- 
blies in which both the shaft and bearing were 
made of identical and very hard materials. 
Some Nitralloy bearings mounted in rubber 
were run at speeds in excess of 75,000 rpm con- 
tinuously for an hour without failure. This was 
all the more amazing, since the bearings were 
not lubricated in any manner whatever. 25 

The high-speed joints of the T-50 were elimi- 
nated by the single unit rotating assembly con- 
sisting of a turbine, the generator rotor, and 
the high-speed shaft. Since dynamic balancing 
required the removal of metal in two planes, 
a brass disk of approximately % 6 - in. thickness 
was fastened below the Alnico rotor. The under 
side of the turbine and this brass disk provided 
two convenient surfaces for the easy removal of 
mass. A special dynamic balancing machine for 
this purpose will be described in Section 
4.6. 

The arming system of the T-132 fuze in the 
original form was to be operated by the impact 
of air so that the fuze would arm after the 
maximum possible air travel. Calculations 
showed this to be approximately 400 yd. This 
would permit the fuze to be fired at 0 incre- 
ments and 45-degree elevation, with the arming 
occurring a very short distance before im- 
pact. 

A manually removable safety pin was pro- 
vided, as shown in Figure 34. This pin was in- 
tended to prevent accidental arming of the fuze 
but had to be removed and thrown away in 
accordance with the customary use of the 
standard trench-mortar mechanical fuzes. In 
the final T-132 designs, a protective plastic 
cover was shrunk over the front end of the 


MECHANICAL DESIGN OF PROXIMITY FUZES 


191 


fuze, and the removal of the pin and the cover 
was accomplished by one motion of the hand. 
Photographs of the arrangement are shown in 
Figure 36. 

Several departures from the bomb and rocket 
arming techniques were made in the details of 
the arming system. The detonator was still 
carried in a detonator rotor mounted above an 
interrupter plate. It was maintained in its safe 



Figure 37. Jolt machine for testing proximity 
fuzes. 


position by an arming shaft, which was with- 
drawn by the action of a screw driven by the 
turbine through a reduction gear train. Its 
movement, however, was not slow as in the case 
of the bomb and rocket fuzes. Instead the deto- 
nator rotor was snapped into position by a coil 
spring. In the T-132 the arming shaft was made 
of Bakelite so as not to short-circuit the an- 
tenna system. It was enclosed in a metal shield- 
ing tube for as great a part of its length as pos- 
sible. In the T-171 a metal shaft was used; a 
short circuit at the antenna was prevented by 
a snap-out motion of this shaft, rapidly with- 
drawing it from the antenna insulator at the 
moment of arming. 


The original design of the detonator rotor 
provided an additional space for a mechanical 
impact detonator element, but because of the 
very great danger in using this element, it was 
not built into the first production of the fuzes. 
Instead the space was occupied by a double- 
element safety pin which held the rotor in a 
safe position unless released by a sustained 
acceleration of over 1,000# (see Figures 6 and 
38). This additional safety was necessitated by 
the requirement that the mortar fuzes be able 
to pass the jolt test. This test consists of mount- 
ing the fuzes by their base threads into a 
machine-driven arm that is subjected to a free 
fall of approximately 3 in. onto a rather hard 
surface for a total of 5,250 drops (see Figure 
37). The fuzes were held in each of three posi- 
tions for 1,750 drops each. It was found that 
the first T-132 and T-171 fuzes built would not 
pass this test but failed by breaking at the an- 
tenna insulator. With the arming system as 
originally designed, this resulted in the with- 
drawal of the arming shaft and the rotation of 
the detonator into the armed position. Since 
the electric detonators are quite safe against 
mechanical shock at handling, this did not nec- 
essarily represent a serious hazard. However, 
the addition of the double-element safety pin 
eliminated even this danger by keeping the 
rotor in the safe position in case of accidental 
withdrawal of the arming shaft. 

Still another version of the arming mecha- 
nism for the T-132 and T-171 series of fuzes was 
designed just before the end of World War II. 
In an effort to increase the unarmed air travel, 
a clock mechanism was substituted for the gear 
train. This clock mechanism, shown in Figure 
38, was mechanically coupled to the detonator, 
and the whole assembly occupied the space 
originally filled by the detonator rotor. The 
detonator was held in the safe position by the 
double-element setback pin described above for 
the original rotor. Upon its release the detona- 
tor was moved into position and was electrically 
and mechanically armed 10 sec after firing. 
This resulted in an automatic increase in the 
safe air travel when the shells were fired with 
the greater number of increments, because the 
air travel to arming now was directly propor- 
tional to the velocity of the shell. 


EGRET 


192 


MECHANICAL DESIGN 


Another great advantage of using this clock 
rotor was the elimination of the gear train and 
arming shaft. This permitted the power supply 
to be completely isolated mechanically from the 
rest of the fuze so that excellent sealing of the 
electronic components against moisture became 
possible. The elimination of the gear train with 


Figure 38. Clock mechanism for arming mortar 
fuzes. Pin assembly in lower right-hand corner 
is common to all fuzes developed for mortar 
shells. It is a double-element inertia device. 

its arming shaft also meant considerable re- 
duction in mechanical vibration and noise. 

Raymond Engineering Laboratories were 
asked to do the engineering and the experi- 
mental production of the clock rotors. 57 Several 
completely satisfactory working samples were 
received from them shortly before the conclu- 
sion of hostilities. 

Another expedient which was experimented 
with for delaying the arming of the fuze for 
as long a time as possible was the use of a 
small dashpot switch ; a cross section of this is 
shown in Figure 39. The switch would be placed 
into the detonator circuit and would normally 
be kept closed by the coil spring. The detonator 
would, however, be kept unarmed by the regu- 
lar clock rotor. Upon firing, the sliding piston 
contact would move back for a distance propor- 
tional to the time integral of the acceleration, 
and, upon cessation of acceleration, it would be 


moved forward by the spring, until it finally 
acted to close the detonator circuit. Since the 
time of the return stroke was dependent on the 
length of the piston travel, automatically vari- 
able arming time could be secured that would 
be controlled by the amount of explosive charge 
used in firing the shell. A considerable amount 
of experimental work was done on this device, 
but it was found that the difficulties in its con- 
struction made it impractical. It was expected, 
for instance, that the effects of temperature 
upon the viscosity of the fluid, one of the sili- 
cones, would be largely canceled out because of 
the double action of the piston; that is, that 
temperature effect on the down stroke and on 
the reverse stroke would be equal. This was 
found not to be the case because the downward 



Figure 39. Diagram of dashpot arming device. 
This device gives longer arming times with larger 
values of setback. 

stroke was extremely rapid, with the flow prob- 
ably turbulent, while the reverse stroke was 
slow with laminar flow. 

The method of making the electric connec- 
tions to the T-132 detonator was another depar- 
ture from the practice followed previously. 
Contact springs were completely eliminated. 
One of the leads of the detonator was grounded 
through the rotor driving mechanism, while the 
other lead acted both as a mechanical stop and 





SECRET 


MECHANICAL DESIGN OF PROXIMITY FUZES 


193 


as the “live” contact. In this manner, the force 
of the rotor driving spring was employed to 
insure good contacts at both detonator leads. 
The details of the detonator rotor and the 
methods of assembling the detonator to the 
detonator rotor are described in reference 23. 
A photograph from this reference is shown in 
Figure 40. 

The electronic assembly of the T-132 in- 
cluded a technique which, while not new in 



Figure 40. Jig for forming and cutting 
detonator leads in mortar fuzes. At bottom of 
photograph are shown from left to right : 
detonator, detonator rotor, detonator rotor with 
detonator installed, bottom view of detonator 
rotor showing lower face of detonator. 

general, was new in the case of proximity fuzes. 
It consisted of painting the resistors and con- 
densers directly upon a ceramic supporting 
member. The antenna insulator was also con- 
structed of ceramic material, and many of the 
oscillator components were also painted di- 
rectly on it. The interconnecting leads and some 
of the plates of the capacitors consisted of 
silver plating on a surface of these ceramic 
members. In the original models of the mortar 
fuze built at NBS the electronic components 
were held between two thin Bakelite plates. 


This general design was copied by the Globe 
Union Company in their design of the first 
ceramic plates. The two plates can be seen in 
Figure 41. 

From tests in the field and in the high-speed 
centrifuge it soon became apparent that the 
weight of the components and the potting com- 
pound above these plates was sufficient to break 
them when under setback. It was immediately 
suggested that it would be better to mount the 
ceramic plates vertically. Several different am- 
plifier assemblies were tested, and it was found 
that a single rectangular plate could support all 
the necessary components with a great saving 
in space. The test terminals were mounted di- 
rectly on one of the edges of this plate, thus 
eliminating the terminal block of the previous 
constructions. A cutaway view of the T-132 
with the vertical plate amplifier is shown in 
Figure 42. 

The antenna insulator was fastened to the 
metal shell of the fuze by soldering it to its 
silver-plated surfaces. In the case of the T-171 
fuze (Figure 43), the ceramic antenna spacer 
was replaced by a mica-filled phenolic antenna 
block, which was molded directly onto the base 
member and which had around its forward sec- 
tion a metal ring, to which the shell of the fuze 
proper was fastened. This construction resulted 
in an extremely rigid assembly, and the later 
models of this fuze as well as of the T-132 suc- 
cessfully withstood the jolt test. 

With the exception of the snap-out shaft de- 
scribed above, the arming systems of the T-171 
and the T-132 were identical. 

The overall dimensions of the T-132 and the 
T-171 were determined as follows. It was de- 
cided to make the mortar fuze fit the standard 
fuze well. The 2-in. diameter was determined 
by the availability of the Zenith generator 
which, at the time, was the smallest available. 
Many shapes of the nose section were tested in 
the NBS wind tunnel, and it appeared that the 
flat nose cap resulted in the greatest stability 
of flight. This cap was, therefore, the one used 
in the initial production. 

When it became obvious that the flat cap re- 
sulted in too great a loss in range and there 
arose the possibility of using tail extensions to 
improve the ballistics, several caps with better 


SECRET 


194 


MECHANICAL DESIGN 





Figure 41. Assembly and principal components of T-132 fuze. Assembly shown uses “horizontal’ 
ceramic plates which were replaced in later models of this fuze. 






MECHANICAL DESIGN OF PROXIMITY FUZES 


195 



Figure 42. Cutaway of T-132 fuze. On right 
center of photograph may be seen vertically 
mounted amplifier used in later models of this 
fuze. See Figure 34 for identification of com- 
ponents. 

lining with the same turbine did not prove 
worth while. 

Mortar Fuze, T-172 

A rather radical departure from the T-132 
and T-171 mortar fuzes was the T-172 fuze 
developed by the University of Florida. In 
order to get a more forward-looking angle of 
sensitivity of the antenna, a loop antenna was 
employed. This meant that the power supply 
and most of the electronic components of the 
fuze did not have to be isolated electrically 


Figure 43. T-171 trench mortar fuze. 

assembly, the overall dimensions of the fuze 
exclusive of the loop were equal to those of the 
T-132. Placing the power supply in the base of 
the fuze permitted the direct coupling of the 


from the body of the shell. It also indicated the 
desirability of locating the generator in the 
base of the fuze so as to permit the use of a 
plastic cap at the base of the loop. A central air 
duct was provided for the intake, and a series 
of round holes near the base of the fuze pro- 
vided the exhaust. The fuze is shown in Figure 
44. By making an extremely compact electronic 


streamlining were designed. The modification 
adapted for the T-132 and the T-171 was the 
132A cap shown in Figure 43 and in Figure 6 
of Chapter 1. Further increases in stream- 


SECRE' 


196 


MECHANICAL DESIGN 


generator shaft to the arming mechanism. The 
gear train was, therefore, located adjacent to 
the detonator, and the whole assembly of the 
gear train and detonator was made to revolve 
into the armed position at the completion of 
400 yd of air travel. 

One of the problems encountered in the de- 
velopment of this fuze was the difficulty of ob- 



Figure 44. T-172 mortar fuze. 

taining sufficient power from the turbine at the 
lowest air velocities. The best shapes of the 
intake were such as to increase the drag of the 
fuze. Compromise solutions had to be em- 
ployed. 61 ’ 72 

A special generator was designed for the 
T-172 (see Figure 45) 72 by the Zenith Cor- 
poration. It was similar to their six-pole T-50 
and T-51 generator but used only three coils. 


By an ingenious method of assembly of the 
stator, the coils were wound directly on the pole 
piece assemblies. Another advantage of the de- 
sign was the fact that the pole pieces were sup- 
ported against setback by a brass ring. This 



Figure 45. Three-coil generator for T-172 
mortar fuze. 


generator was equipped with precision ball 
bearings. The first models of the Zenith T-172 
exhibited several weaknesses in the method of 
supporting the assembled generator, but these 
were soon rectified. 



Figure 46. Cutaway of T-2005 rocket fuze. 

• I 

The end of hostilities prevented any large- 
scale production of the T-172. 

In all three of the mortar fuzes described 


M A 



MECHANICAL DESIGN OF PROXIMITY FUZES 


197 


above, a % 6 -in. thick brass plate was used as 
the interrupter below the electric detonator. 

Rocket Fuze, T-2005 

The success attained with the mortar fuzes 
and the advisability of designing a much more 
universal rocket fuze than the T-30 and the 
T-2004 led to the development of the T-2005. 78 
Since this fuze was intended primarily for the 
Xavy/California Institute of Technology rock- 
ets, its physical outlines were designed accord- 



Figube 47. Schematic arrangement of arming 
mechanism for T-2005 fuze. Arrangement in safe 
or unarmed position is shown on left, in armed 
position on the right. 


ingly. As can be seen in Figure 46, the base 
section extends very little into the fuze well, 
and the main body of the fuze is mounted for- 
ward of the projectile. The general design is 
very similar to that of the T-171. The antenna 
insulator is made broader and heavier, both to 
give increased strength and to result in better 
streamlining. 

The generator power supply is practically 
identical with that of the mortar fuzes. The 
pitch of the turbine blades was, of course, re- 
duced to result in a speed of 20,000 to 80,000 


rpm for projectile speeds of 800 to 3,200 fps. 
It was decided to use precision ball bearings for 
this fuze, since problems of setback support 
and procurement were much simpler than in 
the corresponding cases for the mortar fuze. 

The arming system of the fuze, however, re- 
quires considerable explanation. It was consid- 
ered desirable that the use of any arming wires 
or manually removable pins should be unnec- 
essary, although their use should be provided 
for as optional. The fuze should be capable of 
being mounted on a projectile below the wing 
of a pursuit ship without any danger of being 
armed by the airstream. This naturally re- 
quired that the rotating system of the fuze be 
held from turning until after the firing of the 
rocket. The arming system was to operate 
when subjected to an acceleration greater than 
10 g and perhaps as high as several thousand g. 
This fuze should not arm in less than 300 yd 
under any condition. If the burning of the 
rocket continues beyond 300 yd, the fuze should 
not arm until after the completion of burning. 
An SD element had to be provided that would 
explode the rocket after approximately 6,000 ft 
of air travel. This SD feature had to be optional, 
to be inserted or removed in the field. The fuze 
was to be capable of passing the jolt test. A 
simplified drawing of the main components of 
the arming system is shown in Figure 47. 

A brief description follows: A weight sup- 
ported by a spring and provided with a pin in 
its forward end acts to lock the turbine in the 
fixed position. This weight is normally free to 
move back and forth. When the fuze is fired in 
the normal manner, this weight moves back, 
permitting the air to drive the turbine, the 
shaft of which is coupled to a gear train that 
lifts an arming rod in a manner somewhat 
similar to that in the T-132. This gear train 
also performs another function, that of locking 
down the setback w r eight at the end of 100 turns 
of the turbine. This means that if the 10-# 
acceleration is maintained for a distance of 
roughly 100 yd, the turbine is permanently re- 
leased and can continue to operate and then 
arm the fuze at the end of 300 yd. For high-^ 
rockets, and possibly artillery shells, on which 
this fuze may be used, another weight was pro- 
vided that was retained in its normal position 




198 


MECHANICAL DESIGN 


by a 100-g spring. This high-# weight was in- 
terlocked with the low-# weight described above 
in such a manner that if the fuze experienced 
an acceleration of over 100#, the low-# weight 
would move back first, permitting the high-# 
weight to move and lock it in the lower position. 
This action is identical with that of all the other 
double-element setback devices mentioned pre- 
viously in this report. 

The 300-yd minimum arming distance is not 
affected by this action, so that in all cases the 
T-2005 fuze cannot arm until a safe distance 
away from the launcher. For those cases in 
which the rocket burning continues beyond the 
300-yd mark, a mercury switch is provided 
which keeps the detonator circuit open until the 
forward acceleration ceases. An electric RC 
increases the safe air travel still further. 

Since no double-element setback release was 
provided directly in the detonator rotor, the 
danger of its arming due to the breakage of 
the antenna insulator still existed as it did in 
the case of the original mortar fuzes. Because 
of the low values of acceleration, a small double- 
element safety was not practicable in the det- 
onator rotor. A different mechanism was, there- 
fore, evolved. The arming shaft, instead of 
serving merely as a pin to lock the detonator 
in position, was modified so as to rotate as it 
was withdrawn. This rotation was communi- 
cated to a local arming screw, which also served 
to lock the detonator rotor in the safe position ; 
that is, the arming shaft was used both as a 
lock and as a screw driver. If, while the fuze 
was in the safe condition, the antenna insula- 
tor was broken and the arming shaft fully 
withdrawn, the locking screw would still re- 
main in its safe condition, and the detonator 
would not move. 

The SD was accomplished by a rather simple 
form of differential screw. Two small gears of 
12 and 13 teeth were arranged to mesh with one 
of the pinions of the regular arming gear train. 
These two gears were mounted on a fine screw 
used as their shaft. One of the gears was cou- 
pled to the screw by means of a spline, and the 
other was threaded onto it. In this manner, as 
the two gears revolved slowly at slightly differ- 
ent speeds because of their one-tooth difference, 
the screw was slowly moved downward so as to 


“ground” the firing circuit at the end of several 
thousand feet of air travel. If the use of SD 
was not desired, it was possible to disengage 
the small gears by the simple removal of a 
small screw projecting through the case. The 
whole SD assembly was mounted on a small 
spring, which normally kept it out of engage- 
ment with the driving pinion. 


4 ' 3 '° Miscellaneous Experimental Fuzes 

As mentioned at the beginning of this chap- 
ter, many fuzes were considered and experi- 
mented with that never saw production. Of 
particular interest were the T-40 and T-43 
fuzes, familiarly known as Katrinka, which 
were intended for operation on very large 
bombs. The intention was to use the fin struc- 
ture as part of the antenna loop and to make 
use of the bomb body by shunt excitation. 55 
The fuze itself was to be mounted in a cylinder 
approximately 6 in. in diameter and 12 in. long 
placed inside the fin structure. The energy was 
to be derived from a battery that was to be 
either very well insulated so as to maintain its 
ground temperature for long periods or that 
was to be heated electrically by the plane’s 
power supply. 77 

A small turbine was designed to energize the 
arming mechanism. A feature of this mecha- 
nism of particular interest was the variable arm- 
ing that could be controlled from the plane. The 
arming system contained a differential gear, 
one side of which was driven by the turbine, 
while the other side was connected by means of 
a flexible cable to a control in the plane. The 
output of the differential gear controlled the po- 
sition of the detonator. The flexible cable was 
to serve both for setting the fuze and for releas- 
ing the arming system in the manner similar 
to that of an arming wire. Drawings of the 
mechanical system were made and some of the 
components were actually built, but the project 
was abandoned before a working fuze was con- 
structed. Other fuzes, particularly the T-51, 
appeared capable of fulfilling the application 
for which the T-40 and T-43 were intended. 

Another experimental fuze was intended spe- 
cifically for air-to-air bombing, particularly for 


SECRET 


THE MOUNTING OF FUZES INTO MISSILES 


199 


use with toss-bombing equipment (cf. Division 
4, Volume 2, STR). This fuze was given the 
designation P-4 771B by Bell Telephone Lab- 



Figure 48. Experimental model of generator- 
powered fuze for air-to-air bombing. 

oratories where the development 76 was carried 
out. A particular requirement for this fuze was 
ability to operate satisfactorily at lower air- 
speeds at high altitudes. This resulted in a 


larger turbine system for the power-supply 
generator. Air was directed to the turbine by 
scoop or air duct around the periphery of the 
fuze. A photograph of the fuze is shown in Fig- 
ure 48. Several models were built which operate 
satisfactorily against ground targets. No air- 
to-air tests were conducted and the project was 
abandoned because of the lower priority given 
later in World War II to air-to-air weapons. 


4 4 THE MOUNTING OF FUZES 

INTO MISSILES 

Since the vehicle carrying a radio proximity 
fuze often acts as an antenna and in all cases 
has an effect on the radiation, the method of 
fastening the fuze to the projectile is more 
critical than with contact fuzes. 

For contact fuzes two practices are more or 
less standard. If the fuze is shipped as part of 
the complete round, it is permanently fastened 
in place, usually by staking. Where the fuze is 
inserted into the vehicle in the field, this is usu- 
ally done without any special tools, and hand 
tightening is considered sufficient. No lock 
washers of any kind are employed. 

In the case of proximity fuzes this procedure 
is not tolerable. Loose mounting results in both 
mechanical and electric noise. Extensive studies 
were carried out 6 to determine the best methods 
of mounting fuzes in missiles to reduce both 
mechanical vibration and poor electric contact. 

The M-8 rocket and the mortar fuzes were 
designed to be wrench tightened. The bomb 
fuzes were to be assembled in the field, prefer- 
ably after the bombs were in their racks. To 
insure good electric connections, lock washers 
were specified. Special wrenches were provided 
for all the fuzes. Lugs were provided on the 
fuze housing (cf. Figures 16, 20, and 26) to 
provide anchor points for the wrenches. 

The using Services soon complained that the 
Shakeproof lock washers supplied for the T-50 
fuzes did not permit easy defuzing. Also, there 
was noted on the part of the field personnel a 
tendency to use the dipoles of the T-51 and the 
T-82 as handles in tightening or loosening the 
fuze in its well. Accordingly, a more suitable 
washer was developed. It was manufactured by 


SECRET 


200 


MECHANICAL DESIGN 


the Shakeproof Company and in its outline was 
a duplicate of their external-toothed lock 
washer. Instead of twisting the teeth, however, 
they were bent alternately back and forward. 
This resulted in a spring washer that provided 
considerable friction between the bomb and 
the fuze without a positive lock action. It also 
permitted the operator greater leeway in the 
angular setting of the fuze with respect to the 
bomb for greater convenience in the use of the 
arming wires. Photographs of both the spring 



Figure 49. Washers used for mounting fuzes 
in bombs. Lock washer is shown on the left, 
nonlocking spring washer on the right. 

washer and lock washer are shown in Fig- 
ure 49. 

It was found that the dipoles of the T-51 and 
T-82 were sufficiently strong to be used as 
handles, when this spring washer was em- 
ployed. 


45 SPEED REGULATION 

Very little has been said so far about the de- 
sirability or practicability of automatic speed 
regulation for the various windmills and tur- 
bines used in the Division 4 fuzes. 

There are several reasons why a constant 
generator speed is desirable. 

1. If the generator could be operated at con- 
stant speed at the various velocities of the 
vehicle, electric voltage regulation would not be 
necessary. 

2. The bearing life could be greatly pro- 
longed. 

3. The vibrational forces could be main- 
tained at a minimum, thus increasing the 
amount of permissible unbalance in the rotat- 
ing systems. 

4. The strength requirements of the rotating 
system could be eased, permitting a greater 


choice of materials for the construction of the 
turbine and the rotor assembly. 

5. It would permit the standardization of the 
drive for the fuzes required for different appli- 
cations. 

6. By maintaining a reasonably constant 
speed, the arming system would be in effect a 
time mechanism rather than an air-travel 
mechanism. This would be of particular advan- 
tage because most of the ballistic tables of the 
Services are expressed in units of time. 

In contrast to these obvious advantages there 
is the disadvantage of greater complexity in- 
troduced by the regulating mechanism. This is 
particularly serious, since it is very important 
that the fuzes be capable of withstanding ex- 
treme conditions of temperature and accelera- 
tion. 

It is, of course, obvious that a great many 
mechanisms can be designed to control the 
speed of an air turbine. Yet, at the time of the 
work, no speed control system was known that 
did not require the addition of some moving 
parts and that would depend merely on the 
aerodynamics involved. The matter was dis- 
cussed without success with representatives of 
many companies, who normally engage in the 
construction of pumps and turbine. In the 
summer of 1945, the Douglas Aircraft Com- 
pany of California and the University of Cali- 
fornia engaged in research on the shape of 
nozzles in order to obtain speed regulation for 
the T-172 fuzes. (This work was sponsored by 
the Transitions Office of NDRC.) Their re- 
port 00 concludes that some regulation is pos- 
sible by designing the nozzle in such a way as 
to obtain sonic speeds through the throat. This 
will not give perfect speed regulation since the 
pressure in the throat is roughly proportional 
to the pressure at the nose of the projectile, and, 
therefore, the total mass of the air moving 
through the fuze will vary with the velocity. 
Tests at the National Bureau of Standards on 
a similar mechanism of controlling airflow did 
not give encouraging results. Nevertheless, 
some rather simple mechanisms for controlling 
the speed of propellers were tested, and some 
bomb fuzes equipped with these were actually 
dropped. Perhaps the simplest of these, shown 
in Figure 50, was the mounting of the windmill 


i 


SECRET 


% 


DYNAMIC BALANCING 


201 


on its hub so that it had some axial freedom. 
A spring inside the propeller hub was com- 
pressed when the windmill was driven back 
against the flat nose of the fuze. This effectively 
decreased the airflow and decreased the wind- 



Figure 50. Windmill for speed regulation. 
Normal position of windmill on its shaft (top) ; 
windmill depressed by air pressure (bottom). 

mill speed. The speed regulation, while not per- 
fect, was quite stable. 1 ’ - The disadvantage of 
the scheme lay in the fact that the windmill 
had to be somewhat free upon its shaft, result- 
ing in a relatively large amount of vibration 


and preventing the possibility of good balanc- 
ing. 

The use of flexible blades in the turbines has 
already been mentioned in connection with the 
T-82. Another suggestion to use centrifugal 
regulation came from Zenith and was investi- 
gated by the University of California. 60 

In both the above schemes flexible members 
are employed. These are necessarily located in 
the airstream. Consequently, vibrations of high 
frequency and high amplitude are set up in the 
flexible members, resulting in rapid fatigue. 
Another objection to the flexible blade schemes 
is the difficulty of maintaining accurate dy- 
namic balance at all speeds. 

The overall solution of the high-speed prob- 
lem was the use of well-balanced rotating sys- 
tems, materials of sufficient strength, and the 
proper bearings to permit the rotational sys- 
tem to withstand high speeds without ill effects. 
This method of attack is satisfactory as long 
as the maximum velocity range of the projectile 
is not greater than approximately 4 to 1. As the 
range of velocity of the projectiles equipped 
with similar fuzes is increased much beyond 
that, speed regulation will undoubtedly have to 
be employed. 


46 DYNAMIC BALANCING 

Although the problem of balancing the ro- 
tating system of a fuze may appear to be a pro- 
duction problem, not particularly related to 
fuze development, appreciable work was done 
on the subject by Division 4. While commercial 
equipment for dynamic balancing was available 
during World War II, such equipment was not 
available on the scale necessary for the pro- 
duction envisioned. The commercial equipment 
was both complicated and expensive and could 
not be duplicated by the fuze manufacturers 
themselves. As the fuze program advanced, it 
became more and more evident that the me- 
chanical design of generator-powered fuzes 
could be simpler and fuzes would be more re- 
liable if the rotating systems were dynamically 
balanced. This required that suitable equipment 
be available for doing the balancing in produc- 
tion. 


SECKE 


202 


MECHANICAL DESIGN 


Soon after the T-50 program was started, it 
was found that some units were much noisier 
than others due to the large amplitudes of 
vibrations caused by the rotating systems. A 
process of selection was then applied to the 
windmills before their assembly. A simple un- 
balance tester was built, consisting of a flexibly 
mounted fixture coupled to a crystal pickup, 



Figure 51. Equipment for dynamic balancing 
of vanes of T-50 type fuzes. 


which was fed into an amplifier, the output of 
which was read on a suitable meter. It was soon 
found that it was difficult to distinguish be- 
tween the rotational vibration of the fuze head 
and the noise due to the rather crude ball bear- 
ings employed. A rather sharply tuned filter 
was then introduced into the amplifier, and the 
speed of the windmill was manually adjusted so 
that the rotational vibration was kept at the 
frequency at the center of the amplifier peak. 
In this way, badly unbalanced windmills were 
isolated from the rest. 

It was a simple matter to go from this step 
to a stroboscope, which was triggered by the 
unbalance voltage and indicated the position of 
unbalance. The circuit was so arranged that, as 
the instantaneous unbalance voltage passed 
through zero, it triggered a thyratron which, in 
turn, flashed the stroboscope light. The wind- 


mill appears to stand still under this light. By 
taking a vane and deliberately unbalancing it, 
the equipment can be easily calibrated. A pho- 
tograph of this equipment is shown in Figure 
51. In this method of balancing no effort was 
made to achieve true dynamic balance, but 
since the windmill can be considered to be a 
nearly flat disk mounted at the front end of a 
rather large mass hinged at its base, the re- 
moval of static unbalance in the vane reduces 
the vibration of the large mass to a very low 
figure. In the T-50 production no effort was 
made to balance the rotor of the generator. 



Figure 52. Close-up view of dynamic balancing 
machine for rotating systems of mortar fuzes. 


The equipment described above was em- 
ployed on a large scale by the manufacturers 
engaged in the T-50 fuze program. 

True dynamic balancing was a requisite in 
the construction of the mortar fuzes, and the 
machines of various manufacturers were in- 
spected for suitability. Since the original inten- 
tion in this program was to use ball bearings, 
it was important that the dynamic balancing 
equipment should be able to distinguish be- 
tween ball bearing noise and rotational un- 
balance. 

It was known that the Westinghouse Com- 


CHOICE OF PLASTICS FOR THE PROXIMITY FUZES 


203 


pany had developed a system of “Micro- 
Dynetric” balancing capable of accomplishing 
this. A group of NBS and Bowen engineers 
visited the Baltimore plant of this company and 
witnessed the operation of the only model of 
that machine in existence. The machine ap- 
peared suitable for the purpose, and orders 
were placed by Bowen, Globe Union, and others 
for the procurement of this equipment. It be- 
came immediately apparent that its production 


anced is belt driven at 95 rps. The output of the 
amplifier is fed into a vacuum-tube voltmeter 
by means of which the magnitude of unbalance 
can be determined. The output voltage also 
triggers a stroboscope which locates the posi- 
tion of unbalance. In a later model automatic 
volume control was employed so that no manual 
changes of amplifier gain had to be used for a 
wide range of rotor unbalance. The removal of 
metal was done by hand. 



Figure 53. Dynamic balancing machine shown in Figure 52 and accessory equipment. 


schedule was very much slower than required 
for the fuze program, and NBS undertook to 
design a simple and easily produced balancing 
machine for the project. 9 The machine, photo- 
graphs of which are shown in Figures 52 and 
53, is similar in operation to the standard ma- 
chines of the Gisholt Company and others ex- 
cept for considerable simplification. The rotor 
drive consists of a synchronous motor so as to 
maintain a constant speed. The pickups are two 
standard 2-in. permanent magnet dynamic 
speakers. The amplifier is very sharply peaked 
at approximately 95 c, and the rotor to be bal- 


Modifications in this equipment were made 
by Raymond Engineering, 57 Zenith Corpora- 
tion, 72 and the Bowen Company, 46 for the 
mortar fuze production program. Unbalances 
of the order of 0.05 g-in. could be detected 
readily and corrected. 

True automatic balancing in the sense that 
the balancing machine either adds or removes 
mass in the proper places in the rotating assem- 
bly was, of course, considered, but the pres- 
sure of work and the termination of World War 
II forestalled any work on the several schemes 
suggested. 


SECRET 


204 


MECHANICAL DESIGN 


4 7 CHOICE OF PLASTICS FOR THE 
PROXIMITY FUZES 

T-5 and T-50 Type Fuzes 

One of the problems presented in the con- 
struction of the rocket and bomb proximity 
fuzes was that of determining and developing 
the proper plastic materials to be used in the 
nonmetallic portions of the fuze. 

Some of the basic requirements for suitable 
plastics were high compression strength, high 
impact strength, dimensional stability, and 
good electrical properties at high frequencies. 
The electrical properties included low dielectric 
constant, low power factor, and high leakage 
resistance. The main problem, then, was the 
search for plastic materials with the above 
properties that were commercially available or 
could be produced from materials available in 
large quantities. 

The principal plastic parts of the fuze were 
the insulator nosepiece, to be made of plastic 
material with good electrical properties com- 
bined with good mechanical properties, and the 
oscillator block, for which a plastic with good 
electrical properties was needed. Since the block 
was mounted on a steel plate, high mechanical 
strength was of secondary importance. On the 
other hand, the terminal plate that seals off the 
audio portion of the fuze requires high me- 
chanical strength together with high d-c leak- 
age resistance. The rectifier housing, the det- 
onator rotor housing, and the detonator rotor 
all require a plastic material of high impact 
strength and good dimensional stability. For 
these pieces the electrical requirements are of 
secondary importance. 

In the original choice of material for the 
nosepiece, the electrical requirements had to be 
subordinate to the mechanical requirements be- 
cause of the particular mechanical design 
chosen. There was sufficient space between the 
antenna insert and the body of the fuze to cause 
the electric gradients to be low enough not to 
interfere seriously with the sensitivity of the 
unit. Because of this large space, the effects 
of humidity on the plastic were also of minor 
consideration. Moreover, the high surface 


polish of the molded plastic further reduced the 
effects of humidity by forming a good surface 
seal. 

Dimensional stability, absence of cold flow, 
and high-temperature heat distortion were con- 
sidered points of primary importance in the 
design of the nosepiece. Any looseness would 
be extremely objectionable when the fuze vi- 
brated in operation. Electric noise, which 
would result, would produce a spurious signal, 
causing the fuze to malfunction. One of the 
methods used to fasten the nose to the main 
body of the fuze was the use of knurled steel 
inserts. The use of these knurled inserts pre- 
cluded the use of most of the thermoplastic 
materials, not only because of cold flow, but also 
because the points on the knurling would cause 
stresses which, in turn, would produce crazing 
and so destroy the mechanical strength of the 
piece. When the nosepiece was further modified 
to include the holding of the nose to the base of 
the fuze by through screws, the large compres- 
sional forces under the screw heads were still 
a source of trouble because of crazing. 

Tests of various thermoplastic materials, 
such as methyl methacrylate and styrene, for 
cold flow and crazing, showed that these meth- 
ods were not satisfactory for use with the par- 
ticular design involved. It was determined that 
mica-filled phenolic was the best available ma- 
terial. Various brands of low-loss mica-filled 
phenolic were tested for compression strength, 
creep, electric resistance, dielectric constant, 
and power factor. During these tests it was 
found that the effective impedance of the mica- 
filled phenolic available from the several differ- 
ent manufacturers varied by a factor of as 
much as 2 to 1, although all the material tested 
was submitted as conforming to the same set of 
specifications. 

In the construction of the oscillator block for 
the first fuzes, the same material was used as in 
the nosepiece, because these fuzes (oscillator di- 
ode type [OD] ) had a tuning condenser molded 
into the block. In order to maintain the con- 
stancy of tuning, extremely good dimensional 
stability was required along with freedom from 
effects of humidity. The dimensional stability 
was satisfied by the mica-filled phenolic chosen, 
and the freedom from effects of humidity was 


SE< 


CHOICE OF PLASTICS FOR THE PROXIMITY FUZES 


205 


obtained by finishing the surface of the plastic 
properly. For the more recent fuzes, in which 
the tuning condenser was eliminated, a styrene 
block was used because of its superior electrical 
characteristics and the ability of cement to 
form a better bond with the styrene. The block 
was anchored in place to a metal base plate, 
thus giving the sufficient mechanical strength. 

In the terminal plate a linen-filled phenolic 
was used for its high mechanical strength in a 
thin sheet. In order to preserve high leakage 
resistance, this plate was boiled in wax to seal 
it against the effects of humidity. The main 
function of this terminal plate was to hold the 
components and potting material in the audio- 
frequency portion of the unit. The high leakage 
resistance was made necessary by the fact that 
one of the test leads was part of a circuit, the 
operation of which was affected by a leakage 
resistance of 100 megohms. 

In the mechanical section of the fuze, which 
included the generator housing, the gear train 
housing, the rectifier housing, the detonator 
rotor housing, and the detonator rotor, a high- 
impact phenolic material was used. High im- 
pact strength and dimensional stability were 
the basic requirements. It was later found that 
the dimensional stability of the material was 
not sufficient to take care of the small toler- 
ances required in the generator housing, and 
it was necessary to substitute a pressed metal 
housing. Some difficulty was also experienced 
with the detonator rotor. Consequently, the 
batches which did not maintain their tolerance 
because of poor molding were rejected. 


472 T-51 Fuze 

To modify the T-50 fuze so that the radiation 
pattern would appear directly in front of the 
fuze, it was necessary to use a transverse bar, 
or dipole. In order to conserve developing time 
and reduce as far as possible the need for de- 
signing new components for this fuze, it was 
decided to use as many parts of the original 
bomb fuze as possible. To get sufficient mechan- 
ical strength with this design and to keep the 
overall length of the fuze the same, it was nec- 
essary to mount the dipoles at a much lower 


point on the nosepiece; consequently, the field 
intensity or voltage gradient between the di- 
poles and the metal base of the fuze was much 
higher. Because of these high field intensities 
and because of the desire to obtain greatly in- 
creased sensitivities, it was necessary to obtain 
an insulating material with the best possible 
electrical characteristics. It was already known 
from previous experience with styrene and 
methyl methacrylate that the heat distortion 
point was too low and the material was subject 
to cold flow and crazing. However, because of 
the need for the superior electrical properties 
found only in styrene, a search for a suitable 
modified styrene was made and Monsanto’s 
Styramic 18 was chosen initially. While its 
mechanical strength was lower to a consider- 
able degree than that of the mica-filled phenolic, 
it was felt that it was still sufficient for the 
purpose. Later experience proved that it did 
not have quite the mechanical strength desired, 
and a modification of this material, Monsanto’s 
Styramic 18A, was then used. This material has 
proved to be satisfactory in all respects. 

Later in the development other material 
appeared on the market in quantities sufficient 
for production needs. One of the outstanding 
materials was Dow Q247, which had all the 
desirable mechanical properties of the Mon- 
santo Styramic 18A as well as slightly better 
electrical properties. 


4 7 - 3 T-171 and T-132 Fuzes 

In the T-171 fuze for the 81-mm mortar shell, 
Dow Q247 was used. The higher radiation re- 
sistance of these missiles and the shorter elec- 
tric leakage path (because of reduced size) 
made insulating properties of the plastic a 
prime consideration. At the beginning of this 
project mica-filled phenolics were tried, but the 
sensitivity of the unit was only marginal. In 
this type of fuze the plastic material had to 
support the weight of almost the entire fuze. 
The generator as well as most of the mechanical 
parts had been moved to the nose of the fuze 
to act as an antenna, and the plastic was used 
to mount the oscillator and act as an insulating 
spacer. Because of improved design of the in- 


206 


MECHANICAL DESIGN 


serts, the problem of cold flow and crazing no 
longer had its original importance. In the T-132 
fuze no plastic material at all was used, the in- 
sulating material being a low-loss ceramic. 


474 T-2005 Fuze 

Because of its success in the T-51 bar-type 
fuze, the same plastic material, namely Sty- 
ramic 18A, was used in a fuze designed for the 
Navy rockets. The design was somewhat simi- 
lar to that of the mortar fuze. The generator 
was in the nose portion, and the oscillator was 
built in the leading edge of the plastic antenna 
insulator. If the development of this fuze had 
continued further, possibly a change to Dow 
Q247 would have been desirable, as this ma- 
terial has much higher flexural strength. 

All the components molded of Styramic 18, 
Styramic 18A, or Dow Q247 used in the fuzes 
described above were quite thick and irregular 
compared with the usual piece commercially 
molded. Because of the poor heat conductivity 
common to all plastics and the thickness of the 
sections involved, it was necessary to anneal 
the pieces in order to obtain a strain-free prod- 
uct. This was accomplished by placing each 
complete piece in a tank of hot water and mov- 
ing it into successively cooler tanks as the cool- 
ing took place. The gradual cooling effect thus 
obtained removed internal strains and resulted 
in the production of uniformly strong pieces. 
In order to obtain moldings of sufficient 
strength and density, it was necessary to heat 
the plastic almost to the burning point. The 
molds themselves were run warmer than in 
usual commercial practice. This was done in 
order to prevent too thin a case hardening. All 
the inserts, dipoles, and nose bearings had to 
be preheated in order to prevent too sudden 
cooling as the warm plastic reached those points 
in the mold. 


47,5 Cements 

It was desirable in all cases to eliminate as 
far as possible the electric noise produced by 
mechanical vibration; therefore, the r-f com- 


ponents used in the proximity fuze had to be 
so firmly anchored together that they could not 
be loosened by vibration, temperature variation 
during storage, or any shock experienced by 
the bombs or rockets. 

In order to anchor the different components 
in place successfully, it was necessary to use an 
adhesive possessing certain qualities: low elec- 
tric losses and the elimination of strains and 
lift due to the difference in coefficient of expan- 
sion between the cement and the component to 
which it would be attached. The most fre- 
quently encountered base material on which 
the cement was to be used was mica-filled 
phenolic. 

The styrene solutions which were available 
during the first stages of production presented 
a major disadvantage in their inability to re- 
lease solvents readily. Under infrared heaters 
24 hours were generally required. If the sol- 
vents were still present, the maximum adhesive 
strength could not be obtained, and the sol- 
vents themselves produced electric loss. When 
these styrene solutions did finally become com- 
pletely free of solvents, they became so brittle 
that they would lift upon the slightest shock. 
The latter problem was solved by sand-blasting 
of the base material and, consequently, the 
roughened surface of the mica-filled phenolic 
blocks held the cement mechanically. However, 
the roughened surface, in opening the pores of 
the material, allowed moisture to be absorbed 
much more readily than with the original 
smooth hard surface. Subsequently, greater 
electric loss resulted. Tests were then made 
using a phenolic sirup with powdered mica 
added, which was developed by Globe Union, 
in order to obtain a final coefficient of expan- 
sion of the polymerized mica-filled material 
equivalent to that of the mica-filled phenolic 
block. 

Another approach to the problem was made 
by using a mixture of styrene, polymer, and 
monomer. In this mixture no solvents were re- 
quired to be released, since the monomer poly- 
merized to a solid. It was necessary to add 
polymer to the monomer for two reasons: (1) 
it increased the viscosity of the solution to the 
point where it would stay in place, and (2) it 
would decrease the shrinkage on polymerizing 


•SECRET 


CHOICE OF PLASTICS FOR THE PROXIMITY FUZES 


207 


by the amount of polymer in the solution. When 
modified styrene compounds were used for 
molding the electric sections of the bar-type 
fuze, the styrene adhesive worked especially 
well. The adhesive had the same coefficient of 
expansion as the modified styrene blocks them- 
selves; furthermore, the solvent used formed 
one uniform material. However, the inability 
of the styrene to release solvents readily caused 
the solvent to penetrate the block itself. The 
solvent-release problem was thus even more 
serious than it had been with the use of mica- 
filled phenolic blocks. 

The next advance in the solution of the sol- 
vent-release problem was the substitution of 
plasticized vinyl carbazole, produced by Gen- 
eral Aniline and Film Corporation, for the 
styrene type of adhesive. The solvent release 
time was reduced from about 24 to about 4 
hours. This material had almost as good elec- 
trical properties as the styrene and satisfactory 
mechanical strength. Moreover, because it dis- 
solved in the modified styrene base, its coeffi- 
cient of expansion was not important. 

Dichlorostyrene polymer monomer mixtures 
were also found to be satisfactory because of 
the compatibility in their use with the styrene 
block. One of their important advantages was 
the capacity to form an extremely hard glass- 
like material, with superior electrical proper- 
ties, in about 2 hours. There was, then, no need 
for the release of any solvents. One of the dis- 
advantages of the mixtures was the tendency 
for large forces to be set up upon shrinking in 
polymerizing. This difficulty was eliminated by 
proper plasticizing. 


4/76 Potting 

In a further effort to protect the electric 
components against the effects of temperature 
and humidity and to prevent the production of 
electric noise in the amplifier portion of the 
units, potting material was poured in place. 

The material used had to possess certain 
characteristics. It had to have a reasonable 
amount of elasticity over an extremely wide 
temperature range, low electric losses, dimen- 
sional stability, ease of handling, short poly- 


merization time, and nontoxic qualities. The 
initial material tried was wax. This was un- 
satisfactory because of its low melting point 
and its tendency to sweat at high tempera- 
tures. In order to allow the wax to flow around 
the components readily, a high pouring tem- 
perature was necessary. Consequently, there 
was a tendency for the electrical characteristics 
of some of the components being potted to be 
altered. At low temperatures the forces pro- 
duced by shrinkage were actually sufficient to 
fracture some of the glass components. 

Because of the trouble encountered with 
wax, various addition agents were tried. Two 
different mixtures were finally used. One, de- 
veloped by Zenith Radio Corporation, consisted 
of 80 per cent microcrystalline wax and 20 per 
cent polyisobutylene, molecular weight 100,000. 
This material was used to hold the oscillator 
tube solidly in its tube well. This mixture was 
not too brittle at —40 C and did not flow or 
sweat materially at -{-60 C. 

Another material was a mixture of 20 per 
cent ethyl cellulose, 20 per cent beeswax, and 
60 per cent ceresin. This material did not have 
electrical properties quite so good as the previ- 
ous mixture but was much stronger and had 
good temperature characteristics. It was found 
useful in the centrifugal potting of the genera- 
tor stators in the T-171 fuze. 

The material used largely throughout pro- 
duction was polymerized tung oil. This material 
was not entirely satisfactory. It could be poured 
into the cavities at room temperature and 
would jell in about a half hour. On jelling, it 
became a firm rubberlike mass similar to art 
gum. It had sufficient elasticity to withstand 
shock, and it was firm enough to hold the com- 
ponents in place. It was also sufficiently friable, 
so that it could be broken up with a knife for 
inspection or repair of the units. This material 
was thermosetting. Once set, it would not melt 
at any temperature, and the shrinkage was 
almost nil. 

The polymerized tung oil, however, had 
rather poor electrical characteristics and was 
corrosive toward some of the metallic parts. 
Because of this, the electric components were 
usually coated with a thin coat of wax before 
potting. The speed with which the tung oil set 


SECRET 


208 


MECHANICAL DESIGN 


up depended to a certain extent on the amount 
of moisture present in it. By eliminating this 
moisture, the tung oil set up with much greater 
rapidity. The main advantage of eliminating 
the water from the tung oil was the increase 
in the d-c leakage resistance by a factor of 20 
and the decrease in the power factor by a 
large amount. The dielectric constant was also 
reduced slightly. 

Because of the need for a material with bet- 
ter electrical and mechanical properties, inves- 
tigations were conducted for the development 
of insoluble soaps, such as Glidden PT1 and 
PT2, that could be poured into a unit in the 
liquid state. Saponification would thus occur in 
situ. When these soaps were substituted for 
tung oil, the incidence of certain types of re- 
jects in production was changed from a normal 
11 to 1 per cent. This material, however, had 
disadvantages. Its viscosity, which was higher 
than that of tung oil, somewhat hindered pour- 
ing. Its water resistance was not so good as 
that of tung oil, however, because the material 
was in a closed space. This had no ill effects on 
the operation or storage of the units. Also, the 
material did not have as high a mechanical 
strength as tung oil although it was found ade- 
quate for the purpose. 

Because both of the above materials left 
something to be desired both from the electrical 
and the mechanical standpoint, work was done 
on the use of styrene co-polymers; Dow Q344 
and Dow Q349 are probably the samples of the 
best available material of this kind. All the 
electrical and mechanical properties of the final 
set of these materials were completely satisfac- 
tory. The initial viscosity made them somewhat 
difficult to handle. Furthermore, the surface 
had to be sealed from the air to eliminate 
stickiness as air hindered the surface polymeri- 
zation. These materials were used by the Wur- 


litzer Company for potting the oscillator com- 
ponents of the T-171. 


4 7 7 Solder Flux 

In the examination of a number of units over 
a period of time, units which were maintained 
especially for aging tests, it was found that 
some of the electric measurements in some of 
them were subject to a constant drift. When 
these units were opened and examined, corro- 
sion was discovered around some of the sol- 
dered joints. At first this corrosion was thought 
tp be due to the corrosive action of the tung oil 
potting material, until it was realized that the 
soldered joints were protected from the tung 
oil by a thin wax filament. This corrosion was 
then subjected to a chemical analysis and found 
to be a metal resinate. The resin which formed 
this resinate could have come only from the 
rosin in the solder flux. 

Because of the almost impossible task of re- 
moving all of the flux from the finished soldered 
joint, it was desirable to investigate other 
fluxes which were thought to be less corrosive. 
The corrosion was produced by the absorbed 
oxygen, as the soldered joints were completely 
sealed by wax and tung oil from the air. In 
order to correct this situation, several other 
materials were examined as to their suitability 
for solder flux. One of the materials examined 
is known as polypale rosin, which is a rosin 
dimer. This material absorbs only half as much 
oxygen as is absorbed by ordinary rosin, and 
the corrosive effects are cut down proportion- 
ally. Upon testing, it was found that polypale 
rosin was also considerably superior to ordi- 
nary rosins as a flux because of its superior 
wetting qualities. This material has been used 
in the fuze production with excellent results. 


t SECRET 


Chapter 5 

CATALOGUE OF FUZE TYPES' 


51 INTRODUCTION 

General Remarks 

I N THE PRECEDING CHAPTERS of this Volume, 
there were discussed the general military 
requirements of proximity fuzes, the basic 
theory of operation of radio proximity fuzes, 
and the fundamental principles of design of the 
important parts. The requirements of ideal 
fuzes were defined, and the limitations that 
are imposed by fundamental considerations 
were discussed. It was made clear that a combi- 
nation of fundamental and practical factors 
made it necessary to design different fuzes for 
different purposes. It was shown that the de- 
sign of a fuze was affected by complex prob- 
lems of availability of components and by the 
need to make use of facilities and subassem- 
blies provided by the development and produc- 
tion of fuzes of earlier design. Before launch- 
ing upon a discussion of the manifold problems 
of producing the fuzes in large quantity and 
testing them in the laboratory and in the field, 
it is desirable to present a description of the 
various fuzes that were produced. It is the pur- 
pose of this chapter to provide such a descrip- 
tion. Furthermore, at the expense of some repe- 
tition, the chapter may be read separately from 
the rest of volume, without undue loss of mean- 
ing although frequent reference is made to fig- 
ures elsewhere in the other chapters. 

The description that is given in this chapter 
is intended to provide for each fuze (1) a state- 
ment of the principal applications for which 
the fuze was designed and the limits, so far as 
known, within which satisfactory performance 
may be expected, (2) performance characteris- 
tics under typical conditions, (3) engineering 
data that are useful in the estimation of per- 
formance under certain conditions which are 

a This chapter was prepared by Thomas N. White, Jr., 
with the assistance of Rachel Vorkink, Paul F. Bar- 
tunek, Alan L. Leiner, and Rosalind Schwartz, of the 
Ordnance Development Division of the National Bureau 
of Standards. Bartunek is now with the Physics Depart- 
ment at Lehigh University. 


not covered herein, (4) miscellaneous data on 
important characteristics that distinguish one 
fuze from another, and (5) summary data 
charts for each fuze. For a full understanding 
of the terms used in the development of items 
(3) and (4) above, some reference to other 
chapters may be desirable. Such references are 
indicated in the following presentation. 

Sources of Data and Acknowledgments. The 
scope of the chapter, as outlined above, is some- 
what broader than is demanded by the logical 
development of this report. Information is pre- 
sented that demands substantiation in subse- 
quent chapters. This anticipation of results has 
the advantage that it permits the orderly pres- 
entation, in a single chapter, of the essential 
characteristics and limitations of each fuze. 
Enough has been said in preceding chapters so 
that the data in this chapter can be clearly un- 
derstood. Enough will be given in following 
chapters to show the variations to which these 
data are subject. The discussion of variations 
and difficulties of production, and of testing in 
the laboratory and in the field, can be under- 
stood more readily with reference to the aver- 
age properties of the fuzes as actually pro- 
duced. 

An effort has been made to select data that 
are representative of the bulk of production 
fuzes. Available data on experimental fuzes are 
also included in so far as possible. 

It is important to note that many of the data 
given in this chapter are average values , or 
“best estimates/’ The characteristics of indi- 
vidual fuzes differ more or less from the aver- 
age. A full account of the individual variations 
would lead to undesirable complications in this 
chapter. Discussions concerning the occurrence 
of individual variations and the reliability of 
the estimates are taken up in other chapters of 
this report. 

It is appropriate at this point to acknowledge 
the courtesy of the Ordnance Department and 
the Signal Corps in providing much valuable 
information on the performance of production 
model fuzes in acceptance tests. Much of the 


SECRET 


209 


210 


CATALOGUE OF FUZE TYPES 


most useful and reliable information on fuze 
performance under standard conditions came 
from these sources. Acknowledgment is made 
to these sources and also to the Army Air 
Forces Proving Ground, Eglin Field, Florida, 
the Naval Ordnance Proving Ground, Dahlgren, 
Virginia, and the Naval Ordnance Test Sta- 
tion, Inyokern, California, for special informa- 
tion on certain important experimental and 
service tests. In order to avoid complications it 
has been necessary to omit references to specific 
sources of data in this chapter. The reader can 
obtain a full appreciation of the value of the in- 
formation obtained from military sources only 
by a study of other chapters, particularly Chap- 
ter 9 of this report. 

Scope. The fuzes covered in this chapter are 
primarily those which reached large-scale pro- 
duction. Data on experimental fuzes are pre- 
sented in Chapters 3, 4, and 9 and briefly in 
this chapter in Section 5.6. 

Where the military requirements for per- 
formance are presented in this chapter they 
refer generally to production specifications 
rather than to the original requirements for the 
development project. 

The technical specifications recommended by 
NDRC to the services for production fuzes are 
included in the bibliography. 


0,1 2 Developmental Relations between 
Fuzes b 

The first radio fuze developed was the longi- 
tudinally excited battery-powered T-5, designed 
for use on the 4.5-in. Army rocket M-8 in plane- 
to-plane firing. The T-6 was the same fuze pro- 
vided with an extended arming time to make 
it suitable for ground-to-ground firing on the 
same rocket. 

The first bomb fuzes that were produced in 
quantity were members of the T-50 group. 
These fuzes may be regarded as T-5 fuzes modi- 
fied, as required, by the introduction of a wind- 
mill-driven generator and arming system and 


b The historical aspects of this account are overly 
simplified. For a much more detailed and accurate treat- 
ment, see reference 2 and the history of Division 4, 
NDRC. 


provided with a larger antenna and different 
oscillation frequencies. This antenna, in the 
form of a ring, led to the name ring-type fuze. 
In order to make the most of existing produc- 
tion facilities, the layout of the radio and audio 
circuits of the T-5 were maintained essentially 
intact. Two carrier frequencies, Brown for the 
T-50-E1 production model and White for the 
T-50-E4 production model, were found desir- 
able in order to obtain satisfactory burst 
heights of bombs in the size range 100 to 1,000 
lb. A number of experimental models were 
used, of which the most important were the 
T-50-E10 (Brown) and T-50-E3 (White). 
These were altered from time to time to try out 
changes in the radio and audio circuits and for 
other purposes. The production fuzes T-89, 
T-90, T-91, and T-92 were T-50 type fuzes im- 
proved in certain respects and modified to make 
them more suitable for certain types of bomb- 
ing. 

The rebuilding of the T-5 to provide a group 
of longitudinally excited bomb fuzes was rec- 
ognized at the outset as an expedient, in that 
longitudinal excitation led to a considerable 
dependence of the burst height of the bomb 
upon the conditions of release (altitude and 
speed). This variation in performance was re- 
duced somewhat through the use of a suitable 
amplifier characteristic, but the results repre- 
sented some compromise with ideal require- 
ments. 

Accordingly, at the same time that the ring- 
type bomb fuzes were being developed, work 
was carried on (on a second priority basis) to 
develop a transversely excited (bar-type) c 
bomb fuze, the T-51. In order to take full advan- 
tage of the benefits of transverse excitation, 
considerable effort was made to obtain an am- 
plifier characteristic that was relatively flat 
throughout the expected range of doppler fre- 
quencies. The performance characteristics of 
this fuze were markedly superior to those of the 
ring-type fuzes in certain important respects, 
particularly the relative independence of burst 
height on bomb size and release conditions, and 


c The terms ring- and bar-type were in use so exten- 
sively that they are now retained. The more fundamental 
terms, longitudinally and transversely excited, are used 
for fuzes that did not actually have rings or bars. 

RET \ 


INTRODUCTION 


211 


the greater burst heights attainable. Conces- 
sions to expediency in the matter of using the 
power supply and arming system developed for 
the ring-type fuzes made it possible for the 
T-51 to overtake the production rate of the 
T-50 group within a relatively short time. 

A parallel but slower development, with min- 
imal concessions to expediency, was that of the 
T-82 bar-type fuze. In this development par- 
ticular emphasis was placed on the avoidance of 
disturbances in the radio- and audio-frequency 
systems arising from moving mechanical parts. 
In place of the windmill with its shaft running 
through the radio and audio block, an air duct 
was carried through the block to a base- 
mounted turbine. The T-82 fuze had also other 
advantageous features, but it had not been 
carried into full production at the close of 
World War II. 

The ring-type bomb fuze, which, as men- 
tioned above, had its origin in the fuze for the 
4.5-in. Army rocket, was later modified for use 
on Navy aircraft rockets [AR] and high- 
velocity aircraft rockets [HVAR]. In this case 
the principal structural change was the intro- 
duction of an arming delay mechanism that 
prevented the arming of the fuze until a certain 
time after the burning of the rocket propellant. 
Two types of fuze were produced, both in the 
Brown carrier band. The T-2004 (Mk-172 Mod 
0), intended primarily for plane-to-ground (or 
water) firing with the 5.0-in. AR rocket, was 
in production at a relatively high rate at the 
close of World War II. The T-30 (Mk-171 
Mod 0) for plane-to-plane firing with the 
HVAR, was not so urgently needed and was not 
carried into full production. 

Certain important developmental relation- 
ships are apparent in the structure of the group 
of rocket and bomb fuzes discussed above. An- 
other group of fuzes, the so-called “miniature” 
fuzes, also shows certain close relationships 
among the members of the group. This group of 
fuzes was developed later, and considerable use 
was made of the information obtained during 
the development of the larger fuzes, although 
the structural relationships are not so appar- 
ent. The most advanced member of the minia- 
ture group was the longitudinally excited T-132 
fuze for trench-mortar shells. One outstanding 


characteristic of this fuze, which was rapidly 
approaching the production stage at the close 
of World War II, was the use of circuit connec- 
tions made by painting or spraying material 
through a template onto a ceramic block. Other 
members of the miniature group that were de- 
veloped to a more or less advanced stage were 
the T-171 mortar shell fuze (incorporating 
standard electric components), the T-172 
mortar shell fuze with a loop antenna, and the 
T-2005 general-purpose [GP] rocket fuze. 


Performance Terminology 

Certain important terms used to describe 
fuze performance require definitions. These 
are : 

Proper Function. [Abbrevation : proper or 
P.] A fuze function attributable to normal in- 
teraction between the fuze and target. 

Random Function. A spontaneous fuze func- 
tion, or one not attributable to interaction be- 
tween the fuze and the target. In Chapter 9, 
the random functions are called either “early” 
or “middle” functions for reasons that are there 
made clear. For the purposes of this chapter, 
there is little need for such a distinction and the 
term random function, which has been used 
extensively in the theaters of operation, is 
applied. 

Sympathetic Function. The functioning of a 
fuze caused by the burst of a neighboring vari- 
able-time [VT] fuzed projectile (e.g., in salvo 
or train releases). Sympathetic functions may, 
under certain conditions, be caused by either 
random or proper functions, and in such cases 
are called sympathetic random or sympathetic 
proper functions, respectively. 

Radius of Action [ ROA ]. A measure of the 
proximity to an airplane, or like target, within 
which reasonably reliable functioning of a VT 
fuze can be expected. The ROA is usually de- 
fined as the radius of a cylinder, with axis 
parallel to the trajectories, within which a 
specified percentage of proper functions should 
occur. 

Afterburning. (In connection with rockets.) 
Burning of residual propellant after the end of 
the main blast. Afterburning that persists be- 


SECR 


212 


CATALOGUE OF FUZE TYPES 


yond the fuze arming period is conducive to 
random functioning of the early variety. After- 
burning is aggravated by conditions such as 
low temperature or inadequate charge that 
bring about inefficient combustion of the pro- 
pellant. The phenomenon of random function- 
ing caused by afterburning is complex and not 
yet understood in full detail. For a thorough 
discussion of the subject, see Chapter 9. 


Preparation of Fuzes for Use 

For all fuzes that were produced on a large 
scale, Army and Navy manuals are available 
in which full details are given on the prepara- 
tion of the fuzes for use. For the Army rocket 
fuzes see references 5 and 6. These fuzes are 
preferably checked shortly before use by means 
of field test equipment which is described in 
the bulletins. For the ring-type and bar-type 
bomb fuzes, instructions are given in refer- 
ence 7. For Navy rocket fuzes, see reference 4. 
Some of the descriptive material in this chapter 
has been taken from these manuals. 


Safety and Arming 

All VT fuzes have two common safety fea- 
tures: (1) an off-line powder train, and (2) an 
interrupted electric detonator circuit. It is the 
purpose of the arming mechanism to line up the 
powder train and to complete the electric det- 
onator circuit after the projectile has traveled 
to a safe distance. In considering the general 
characteristics of the various arming mecha- 
nisms, it is convenient to divide the fuzes into 
two classes: (1) fuzes for relatively non- 
accelerated projectiles (bombs), and (2) fuzes 
for accelerated projectiles (rockets, mortar 
shells) . 

1. All the fuzes for relatively nonaccelerated 
projectiles have a windmill-driven generator 
and arming mechanism. In these fuzes the 
windmill or vane (see footnote h Section 3.4.5) 
must be turned a definite number of revolutions 
in order to arm the fuze, and also, after arm- 
ing, the vane must be turning at a certain mini- 
mum rate in order to provide sufficient voltage 


to sensitize the fuze. For projectile speeds with- 
in a fairly wide range, the rotational speed of 
the vane is very nearly proportional to the 
speed of the projectile, so that the distance 
along the trajectory to arming is practically 
independent of the speed of launching. How- 
ever, since the ratio of. vane speed to projectile 
speed is not the same for all sizes and shapes 
of projectiles, the air travel to arming is not the 
same for all fuze-projectile combinations. 

2. All the fuzes for accelerated projectiles 
are so designed that acceleration in the proper 
direction is required for arming. These fuzes 
will not arm if subjected to an acceleration that 
.is substantially less than the minimum to be 
expected with the projectiles on which the fuzes 
are to be used. Furthermore, it is necessary 
that the acceleration should persist for a cer- 
tain minimum time, i.e., that the projectile 
should attain a certain minimum velocity be- 
fore arming can occur. Other arming require- 
ments differ for the different types of fuzes, 
varying from a fixed arming-time requirement 
for Army rocket fuzes to a fixed air-travel re- 
quirement for mortar shell fuzes. 

All fuzes having an arming vane are 
equipped with an arming pin which prevents 
the vane from turning until the projectiles are 
released. 

An additional safety feature used on some 
models is the safety pin. The safety pin is in- 
serted into the arming mechanism through an 
opening in the booster cup. The pin cannot be 
inserted unless the arming components are in 
the safe unarmed position. Each fuze comes 
supplied with this pin in place and the fuze 
cannot be inserted into the fuze well unless the 
pin is removed. A most important feature of 
the safety pin is that fuzes whose seals have 
been removed can have the arming mechanism 
checked for safety in the field. 

The arming features are built into the fuzes 
and can be altered only by breaking seals or by 
other deliberate action. Although no adjustable 
arming mechanism is provided in the fuzes, it 
is possible to extend greatly the air travel re- 
quired to arm most of the bomb fuzes by the 
use of an accessory device called an “arming 
delay” (see Figure 1 of Chapter 4). This de- 
vice is set for the desired delay distance and 


SECRET 


FUZES FOR THE ARMY 4.5-IN. ROCKET 


213 


is clipped onto the bomb fuze. After the set 
delay distance has been traversed the delay 
device is thrown off, releasing the arming vane. 
From that point on arming proceeds in the 
usual fashion. 

All fuzes are detonated by the discharge of a 
condenser through an electric detonator. After 
the condenser has been charged, it may remain 
charged for some time even if the source of 
electric power ceases to function. For this rea- 
son, fuzes which are known to have been 
armed, such as duds found on the ground, 
should not be handled for one hour after the 
vanes have stopped rotating. Duds should be 
handled only by qualified bomb disposal officers. 


5 2 FUZES FOR THE ARMY 4.5-IN. ROCKET 
521 General 

Military Requirements 

The Army M-8 rocket and the VT fuze for it 
were developed at about the same time under 
conditions of great urgency, primarily as a 
means of defense against bombing attacks. The 
VT-fuzed rocket was to be fired from fighter 
planes against bomber formations. Although 
the original requirement prior to development 
was for a 50 per cent fuze, it was required for 
production items that at least 65 per cent of the 
fuzes should function if the rockets passed 
within approximately 60 ft of a target plane. 
It was required also that the fuze should oper- 
ate at a point on the trajectory such that effec- 
tive use would be made of the lateral concentra- 
tion of fragments from the rocket. Since the 
relative velocities of rocket and target, the 
angle of attack, and the structure of the target 
were all variable, it was not practicable to 
specify any sharply localized set of burst posi- 
tions. In general, however, it was desired to 
have the rocket burst just before it arrived 
closest to the target plane (see Section 1.3). 

The VT-fuzed rocket was later shown to have 
properties that made it adaptable for use in 
strafing operations or in ground artillery oper- 
ations, but it was not designed for these pur- 
poses. 

Although it is not within the scope of this re- 


port to detail the characteristics of the rocket, 
some remarks on this topic are required to per- 
mit a balanced assessment of the usefulness of 
the fuze. In particular it should be noted that 
the rocket was not adapted to precision shoot- 
ing. As a result, even with a perfect fuze the 
probability of disabling an isolated enemy tar- 
get plane would have been appreciably reduced 
by the dispersion. 

Fuzes and Rockets 

The T-5 and T-6 VT fuzes for the 4.5-in. 
Army rockets are intended for use as indicated 
in Table 1. 


Table 1 . Application of T-5 and T-6 fuzes. 


Fuze 

Use 

4.5-in. rockets 

PD, T-5 

Plane to plane 

M-8, M-8A3, T-22, T-74, 


Plane to ground 

(M-8A1, M-8A1B1, 


Plane to water 

M-8A2)* 

PD, T-6 

Ground to ground 

M-8, M-8A3, T-22, 
(M-8A1, M-8A2) f 


* Fuze T-5 should be used in these rockets only when the fins have 
been notched (see reference 6, paragraph 10), or when modified by 
4.5-in. aircraft rocket kit T-23. 


t T-6 fuze should be used on these rockets only when the fins have 
been notched (see reference 5, paragraph 10). 

The fuzes T-5 and T-6 screw directly into all 
standard loaded 4.5-in. rockets listed in Table 1. 
They are directly interchangeable with the 
PD M-4 series of rocket contact fuzes both 
physically and ballistically. The fuze as issued 
is not complete. A battery must be installed 
prior to use. The standard components of a 
fuze are shown in Figure 12 of Chapter 4. 
Figure 1 shows 4.5-in. rocket M-8 fuzed with 
T-5. The fuze T-5 has a 1-sec arming time ob- 
tained through use of the switch SW-230A or 
SW-230C, 1.0-sec arming. The fuze T-6 arms 
in 3 to 6 sec, by using the switch SW-230A or 
SW-230C, 5-sec arming. The only other differ- 
ence between the T-5 and T-6 is that the T-5 
contains a self-destroying feature that will 
detonate the rocket approximately 6 to 12 sec 
after being fired if the fuze has not already 
functioned on a target. 

General Limitations 

The fuzes may be used during day or night 
and are not affected by fog or clouds. Heavy 


SECRET 


214 


CATALOGUE OF FUZE TYPES 


rain will increase the number of random func- 
tions and duds. On account of the use of dry cell 
batteries as a power supply, extreme tempera- 
tures must be avoided. Satisfactory operation 



Figure 1. T-5 fuze on M-8 rocket. 


can be expected in the temperature range from 
20 to 100 F. 

The fuzed rockets may be fired in ripple salvo 
without sympathetic functioning caused by 
random bursts. 

The requirement for notching of the fins, 
mentioned above, is introduced because some of 


the M-8 rockets were manufactured with fins 
that did not lock in the open position. Any rat- 
tling or vibrating electric conductor on the sur- 
face of the rocket, which is part of the radiat- 
ing system of the fuze, is likely to cause electric 
disturbances that will detonate the fuze. In 
notching the fins on the rockets that require 
this treatment, care must be exercised to avoid 
excessive twist of the fins. Otherwise the rock- 
ets may be caused to spin at a rate that will 
delay the operation of the arming switches (see 
following section). This precaution is of con- 
siderably greater importance in the use of the 
T-5 than in the use of the T-6 fuze. 

The T-5 fuze is susceptible to random func- 
tioning under conditions that aggravate after- 
burning of the rocket propellant. One type of 
propellant trap that was used during the de- 
velopment of the rocket was found to be con- 
ducive to a high incidence of random functions 
about 2 sec after firing. This particular trap, 
characterized by a double ring of wire at the 
rear end, was not used in the final rocket de- 
sign. 


Functioning Characteristics 
Safety, Arming, and Self-Destruction 

The arming of the fuzes is controlled by a 
mechanism that delays the arming for a certain 
period of time after the end of the acceleration 
that occurs during the burning of the rocket 
propellant. A detailed description of the me- 
chanical arming is given in Chapter 4 and of 
the added RC arming in Section 3.3. The arm- 
ing distance thus depends upon the velocity of 
the rocket prior to arming. The velocity of the 
rocket is dependent upon a number of factors, 
such as weight of the round, the amount and 
temperature of the propellant, and the speed of 
the plane if the rocket is fired from a plane. 
There are also variations from fuze to fuze in 
the arming distance, on account of tolerances 
permitted in manufacture. The reader is re- 
ferred to Chapter 9 for a discussion of these 
factors. For the present purpose it is. sufficient 
to give as arming distance the minimum dis- 
tance at which arming will occur under any 
reasonable conditions of firing. 


SECRET 


FUZES FOR THE ARMY 4.5-IN. ROCKET 


215 


In determining the minimum range from 
which VT-fuzed rockets can be fired profitably, 
it is necessary to know the maximum arming 
distance, namely that distance at which all the 
fuzes will be armed. This distance also depends 
upon a number of factors, but a reasonable 
upper limit can be given. 

The arming switch is so designed that it can- 
not be operated by violent jolts, nor can it be 
assembled into the fuze unless it is in the safe 
position. Although very unlikely, arming is not 
impossible in case of rocket blowup, and after 
such events fuzes should be disposed of only by 
trained personnel. This statement applies also 
to dud fuzes. 

The self-destruction [SD] feature mentioned 
above is incorporated into the T-5 fuze pri- 
marily as a safeguard against operation as a 
ground-approach fuze when used over friendly 
territory in case it does not operate on a target. 

The arming mechanism was not designed for 
a spinning rocket. As mentioned above, exces- 
sive twisting of the fins during the notching 
operation required by a few of the rockets can 
cause a spin that will interfere with proper 
switch operation. Experience has shown that if 
the fins are not twisted in excess of 2 degrees 
no trouble will be encountered (see Section 9.2 
for details) . 

For the T-5 fuze, the risk of a random burst 
within certain specified distances is indicated 
in the following table. 


Minimum range (yd) for plane-to-plane use, 
both planes the same speed. 


Plane 




speed 


Attack 


(mph) 

Pursuit 

from side 

Head-on 

300 

243 

390 

537 

400 

235 

430 

625 


For the T-6 fuze the probability of arming 
within certain specified distances is given be- 
low. The distances that are of practical interest 
are the horizontal distances for minimum 
quadrant elevation [QE]. 

Horizontal distances Probability of 
from launcher arming 

(yd) (percent) 

840 nil 

900 1 

960 5 

The minimum firing range is determined 
primarily by the need to use a QE large enough 
to carry the just-armed fuze so high that it will 
not function on the ground signal. The mini- 
mum QE and range are 8 degrees and 1,600 
yd. Another reason for placing a lower limit 
on the QE is in order to avoid excessive burst 
heights (see following section on ground-to- 
ground firing of the T-6). 

Proximity Bursts in Plane-to-Plane 
Firing of the T-5 


Distance from 
launcher 
(yd) 

175 

210 

250 


Risk of 

random function 
(per cent) 

nil 

1 

5 


In aerial combat the position of the target 
plane will change appreciably during the arm- 
ing of the fuze so that allowance must be made 
for the relative velocity of the attacking and 
target planes in estimating minimum firing 
ranges. A representative table of minimum fir- 
ing ranges follows. At these ranges a negligible 
percentage of the fuzes are unarmed. The 
values given for broadside approach are appli- 
cable in plane-to-ground firing. 


The radius of action of the fuze is about 60 ft 
for attack on a medium bomber from the rear. 
For other forms of attack, it may vary some- 
what, in the manner indicated in reference 6, 
Figure 2. On the average at least 75 to 85 per 
cent of VT-fuzed rockets within ROA can be 
expected to yield proximity bursts. The lower 
percentage is to be expected at extreme range 
on account of greater losses through random 
functioning during the longer flight. 

The distribution of bursts about an airplane 
target is too complex for description here (see 
Section 9.2.3). In general it may be stated 
that for a round that passes very close to a 
part of the target, e.g., the tail, the burst will 
occur almost opposite that part of the target. 
For rounds that pass close to the ROA, the 


SECRET 


216 


CATALOGUE OF FUZE TYPES 


burst is likely to occur about opposite the center 
of the target. 

Plane-to-Ground Firing of the T-5 

The mean burst height varies considerably 
depending upon the dive angle (see Figure 31, 
Section 5.5). It should be noted that for shallow 
dives the bursts are very high and widely scat- 
tered, diminishing considerably the accuracy 
of placement of the bursts and the damage to 
be expected. For best results, dive angles should 
be in excess of 30 degrees. 

Ground-to-Ground Firing of the T-6 

Variation in burst height with firing QE is 
shown in Figure 32, of Section 5.5. It may be 
seen that, for angles of 30 degrees or less, 
heights obtained over ground would center 
around 70 ft with a very large scatter. Effect- 
field tests have indicated that such a height 
would be excessive under most conditions. To 
obtain more satisfactory heights, therefore, 
firing elevations should be about 40 to 50 de- 
grees. 


5 - 2 - 3 Structure 

General Arrangement 

The nose member (MC-382) of the fuze, 
comprising the electronic system, is outlined 
by a hollow conical plastic shell mounted on a 
metal platform which supports the r-f oscillator 
block inside the shell (cf. Figure 12, Chapter 
4) . The amplifier section is potted inside a thick 
metal skirt which extends down from the plat- 
form. The tip of the conical shell is metallic 
and serves as antenna for the fuze. 

The battery member (BA-75), outlined by 
an insulating container, comprises an axially 
located A supply cell nested in a cylindrical 
firing condenser which is surrounded by six 
stacks of B supply cells and one additional A 
supply cell. 

The switch member (SW-230C), also cylin- 
drical in outline, contains an acceleration- 
operated mechanism for closing the A and B 
circuits and for delayed closing of the firing 
circuit and alignment of the powder train. In 
the switch is located the electric detonator, a 


tetryl lead, and in some switch models a me- 
chanical SD switch. 

The nose and switch carry projecting con- 
nector pins and the battery, located between, 
has corresponding socket holes on each end. 
The three members, when plugged together, are 
screwed into a housing (M-381) which con- 
tains a tetryl booster charge at the bottom. 
This then comprises the complete fuze, T-5 
or T-6. 

Arming Mechanism 

The arming process is completely controlled 
by the mechanism contained in the switch 
SW-230C. The mechanism is based on a new 
acceleration-integration principle developed at 
the National Bureau of Standards [NBS] and 
fully described in Chapter 4. The switch will 
not operate unless subjected to an acceleration 
greater than 75# in the proper direction for a 
time greater than 0.15 sec. (The principal ele- 
ments of the switch are shown in Figure 5, 
Chapter 4.) In brief, the operation is as fol- 
lows : The acceleration, acting on a weight 
eccentrically located on the driving shaft of the 
switch turns the shaft 90 degrees against the 
force of a 75 -g spring. This motion is retarded 
by an escapement wheel and flutter-bar (see 
left-hand view in Figure 5, Chapter 4). At the 
end of the 90-degree turn, a spring-loaded 
rotary switch (center view) is allowed to snap 
shut (right-hand view), closing the A and B 
battery supply circuits of the fuze. When accel- 
eration ceases, a rack-toothed slider-bar is 
driven by means of a pinion gear over to the 
other side of the switch, closing the firing cir- 
cuit contacts which are located at the end of 
the slider channel, and also aligning a tetryl 
plug in the slider with an electric detonator 
which lies at the center of the channel. The mo- 
tion of the slider is retarded by the same 
escapement mechanism to the extent of 0.7 sec 
or more. Additional arming is provided in some 
of the SW-230C switches by insertion of a 
resistor in the thyratron-condenser circuit. 
This delays the time at which the condenser 
will acquire sufficient energy to fire the detona- 
tor. Arming times up to about 6 sec are secured 
in this manner. The total arming time is 
stamped on the SW-230C switches. 




FUZE FOR NAVY ROCKET AR 5.0 


217 


Self-destruction of the T-5 is accomplished 
either by an RC circuit containing a special 
neon bulb NE-23 or by a mechanical switch. 
The circuit for the RC-SD consists of a 30- 
megohm resistor connected from B-f- to a 
0.25-mf condenser, the other side of which is 
grounded (see Figure 52, Chapter 3). From 
the common point of resistor and condenser, 
the neon bulb connects to the thyratron grid 
feed line at a point between R-15 and R-16. The 
mechanical SD is illustrated in Figures 4 and 
10, Chapter 4. 

R-F System 

The oscillator diode [OD] circuit used in the 
T-5 and T-6 fuzes is shown in Figure 2. Values 
of the components are given in Table 2. 


Table 2. Component values for oscillator in T-5 
and T-6 fuzes.* 


Resistor 

(R) 

Value 

Con- 

denser 

(C) 

Value 

(mmf) 

Coil Notes 
(L) 

1 

0.1 megohm 

1 

50 

1 

6 turns 

2 

15,000 ohm 

2 

50 

2 

6 turns 

3 

10 ohm 

3 

variable 

3 

5 turns 

4 

0.1 megohm 

4 

50 

4 

r-f choke 

5 

1.0 megohm 

5 

50 

5 

r-f choke 



6 

50 

6 

r-f choke 



18 

50 




Triode: QF 200 C or SA 780 A 
Diode: QF 197 


* Switches SI and S2 are not located in the oscillator section, but 
in the SW-230 switch section; C18 is located in the amplifier section. 

The oscillator components are assembled on 
a phenolic block much as illustrated in Figure 
5, Chapter 6. The circuital relation of the com- 
ponents can perhaps be visualized better from 
Figure 13, Chapter 3. Both illustrations are 
actually of the T-50, as evidenced by the central 
hole for the generator shaft; exact details of 
the T-5 oscillator block are given in reference 1. 

Amplifier 

Except for a few minor elements, the ampli- 
fier circuit of the T-5 and T-6 fuzes is shown 
in Figure 25, Chapter 3, to which Table 3 
applies. The missing elements are noted in the 
table. 


Table 3. Component values for amplifier in T-5 
and T-6 fuzes. 


Resistor 

(R) 

Value 

(megohm) 

Condenser 

(C) 

Value 

(mf) 

6 

1.0 

7 

0.02 

7 

0.15 

8 

50 mmf* 

8 

1.0 

11 

0.001 

9 

3.3 

12 

250 mmf 

10 

0.68 

13 

0.001 

11 

1.0 

14 

0.002 

12 

1.0 

16 

0.01 

13 

1.0 



14 

3.3 

Coil 

Turns 

15 

2.2 

(L) 


16 

0.1 

5 

70 

17 

4.7 

6 

19 in. of No. 32 

19 

Of 


advance wire 
wound on C9 
(resistance and 
inductance 
shown in Fig- 
ure 9) 


Pentode: QF 206 or SA 781 A.f 
Thyratron: GL 489 (GE) or SA 782 B.y 


* The following three 50-mmf by-pass condensers do not appear on 
Figure 9, Chapter 3; pentode grid, pentode filament, thyratron grid 
to ground. 

t For SA 782 B, make R17 = 0 and R19 = 2.0 ohm. 

X For SA 781 A, make R15 = 1.0 megohm, R9 = 4.7 megohm, and 
C14 = 0.005 mf. 


5 3 FUZE FOR NAVY ROCKET AR 5.0 

531 General 

Military Requirements 

The VT fuze designed for plane-to-surface 
application of the AR 5.0 rocket was required 
to give the following performance: (1) proper 
function scores should be on the average 
greater than 70 per cent, and (2) burst heights 
should lie within the range 10 to 100 ft. 


Fuze and Rocket 

Designations for fuze and rocket parts are as 
follows : 


Fuze 

Rocket 

Motor 

Head 

T-2004 Mk-172 

AR 5.0 

3.25-in. 

5-in. 

ModO 


MK-7 

MK-1 

(Army (Navy 





designa- designa- 
tion) tion) 

The fuze is a modified ring-type bomb fuze 
and in external appearance is identical with 


SECR 


218 


CATALOGUE OF FUZE TYPES 


the T-50 models. (It requires a larger cavity 
than the MK-149 or other rocket nose fuzes 
and is, therefore, not interchangeable with 
them.) See Figure 3 for complete round, T-2004 
on AR 5.0. The principal structural change was 
the substitution of a setback gear train in place 
of the bomb fuze gear train. The function of 
this gear train is to complete mechanical arm- 
ing at the end of the burning period. A second 


energy to fire the detonator. In firing at short 
range, this can cause duds. 

Functioning Characteristics 
Safety and Arming 

The mechanical arming mechanism is de- 
scribed fully in Chapter 4. Additional time de- 



Figure 2. Oscillator-diode circuit used in T-5 and T-6 Army rocket fuzes. 


change was the introduction of a delay that 
prevented arming of the fuze until a certain 
time after burning of the propellant had 
ceased. 

General Limitations 

The fuzes may be used at any temperature 
at which the rocket can be used. They are not 
affected by clouds, fog, snow, or light rain but 
may be affected by heavy rains or hail. 

Afterburning of the rocket propellant may 
cause early functions if the fuzes are armed. 
Another effect of serious afterburning is to 
cause repeated dumping (see Section 3.3) of 
the firing condenser before it has sufficient 


lay in arming is introduced by charging the 
firing condenser through a resistor. The maxi- 
mum and minimum arming distances are 1,500 
and 1,000 ft when a 1.5-megohm resistor and 
1.0-mf firing condenser are used. 

From the standpoint of safety the actual dis- 
tribution of early bursts is pertinent. Field test 
results give the following: 

Early functions Distance to burst 

per cent of total rounds fired (ft) 

0 1,400 

1 2,300 

1.5* 3,200 

* Based on 2,006 rounds. 

The minimum release range (to insure arm- 
ing) is a function of rocket temperature and 



FUZE FOR NAVY ROCKET AR 5.0 


219 


plane speed. The effect of these parameters on 
the minimum release range is shown in Fig- 
ure 4. 

Burst Heights 

The average fuze is designed to function 30 
to 40 ft above ground when fired from a plane 
in a 40-degree dive. However, functions at 15 
to 60 ft (or considerably more over water) 



Figure 3. T-2004 fuze on AR 5.0 rocket. 

may be expected because of variations in the 
nature of the terrain and of variations among 
individual fuzes. 

Curves showing variation of burst height 
with angle of dive are given in the data sheets 
of Section 5.5. Because of the dependence of 
range dispersion upon dive angle, values of 30 
degrees or greater are recommended. 


53,3 Structure 

General Arrangement 

The layout of the T-2004 is identical with 
that of the ring-type bomb fuzes (see Section 
5.4.3). 

Arming Mechanism 

The arming scheme of the T-2004 is essen- 
tially the same as that of the ring-type bomb 
fuzes (Section 5.4.3) except for the mechanism 
that operates the slow-speed shaft and the in- 
troduction of RC delay, as used in the T-6 
Army rocket fuze. The slow-speed shaft is con- 
trolled by a device that occupies the same space 


as the gear train of the bomb fuze but which 
is a combination of a gear train and an accel- 
eration-operated system of levers and locks, 
as shown in Figure 29, Chapter 4. To obtain 
arming, the vane must turn a predetermined 
number of revolutions during an acceleration 
in the proper direction of more than lOp. The 
spring-loaded slow-speed shaft is provided with 
a toothed lever arm which is entrained with the 
vane shaft by a worm gear system. If the vane 
is turned too much in the absence of adequate 
acceleration, the lever is forced against a lock, 
and the gear train strips at such a point that 
subsequent removal of the lock by acceleration 
will not free the slow-speed shaft. Adequate 
acceleration during the turning of the vane 
removes this lock. The weight which operates 
the locks is shown in the unaccelerated position 
(upper left of Figure 29, Chapter 4), and the 
accelerated position (upper right of figure). 
As soon as the slow-speed shaft is freed from 
the gear train, the spring rotates it 90 degrees. 
At this position further motion of the slow- 
speed shaft lever arm is blocked by a projection 
on the weight. As soon as acceleration falls to 
a low level, this block is removed, and the slow- 
speed shaft is snapped around by the spring an 



Figure 4. Minimum release range for T-2004. 


additional 90 degrees into the armed position. 
Since there is no further motion of the shaft, 
a transfer pin is unnecessary, and the detona- 
tor rotor is permanently locked to the shaft. 

The fuze is mechanically armed and the fir- 
ing circuit is closed at the end of acceleration 
of the rocket. Detonation cannot occur until 
somewhat later, however, on account of the RC 
delay in the charging circuit of the firing con- 
denser. 


SECR 


220 


CATALOGUE OF FUZE TYPES 


R-F System 

The oscillator diode circuit of the T-2004 
fuze is the same as that of the bomb fuzes con- 
taining the OD circuit (see Section 5.4.3) 
except for the addition of 50 mmf to the capac- 
ity of all the by-pass condensers. 

Amplifier 

The amplifier circuit of the T-2004 fuze is 
the same as that of the bomb fuzes (see Section 
5.4.3), except for the addition of a 0.02-mf 
condenser and 0.33-megohm resistor in series 
from the pentode grid to ground, in order to 
reduce the gain of the amplifier. The resistors 
in the feedback network are altered to give a 
suitable peak amplification frequency and a 
number of minor changes in circuit component 
values are introduced. These changes are shown 
in Table 4 which gives values that differ from 
those of the amplifier No. 11 of the T-50-E4 
bomb fuze (see Table 8) . 


Table 4. T-2004 amplifier component variations 

from T-50-E4 amplifier 11. 


Resistor 

(R) 

Value 

(megohm) 

Condenser 

(C) 

Value 

(mmf) 

11 

0.68 

10 

20,000 

12 

0.68 

12 

500* 



13 

1,000 



14 

2,000 


* See text regarding addition to circuit. 


Power Supply and Firing Circuit 

The power supply and firing circuit (Figure 
77, Chapter 3) used in the Navy rocket fuze 
is nearly the same as that used in the bomb 
fuzes. The main difference is the introduction 
of RC delay. The thyratron plate and one deto- 
nator contact spring are connected to B-f- 
through a high-resistance R27 (0.51 megohm, 
nominal). The other detonator contact spring 
is connected, through the firing condenser C20, 
to ground. On completion of the detonator cir- 
cuit, the firing condenser is charged at low 
current through the detonator. The other dif- 
ference, made possible by improvements in con- 
denser construction, is the use of an additional 
filter condenser, C23. 


5 4 BOMB FUZES 

5,4,1 General 

Military Requirements 

The military requirements for VT bomb 
fuzes may be classified as (1) requirements for 
GP fuzes, and (2) requirements for fuzes in- 
tended to be used for specific purposes (e.g., 
the enhancement of the blast effect of a certain 
bomb). Generally speaking, the requirements 
of the second kind were specified after the 
properties of the fuzes had been well estab- 
lished, and these requirements can be described 
with some accuracy. On the other hand, the re- 
quirements for GP fuzes did not remain fixed 
throughout the course of development, and the 
description of these requirements cannot be 
given completely without introducing an unde- 
sirable amount of historical detail. 

This is particularly true in the case of the 
ring-type fuzes. For example, the initial re- 
quirements of uniformity of burst heights were 
such that engineering calculations indicated 
that it would be necessary to manufacture 
ring-type fuzes in three different carrier-fre- 
quency bands in order to cover the specified 
range of bomb sizes. Certain compromises were 
made and the ring-type fuzes were manufac- 
tured in only two carrier bands. Later, the ad- 
dition of Navy requirements to the existing 
Army requirements led to the manufacture of 
two types of fuzes in each carrier band. 

Largely as a result of knowledge gained from 
effect-field tests, and service experience on the 
relative usefulness of different types of bombs, 
it gradually became apparent that uniformity 
of burst heights for a wide range of bomb sizes 
and release conditions was not so important as 
had originally been supposed. In essence, it was 
concluded that under many conditions the 
effectiveness of an air burst was so much 
greater than that of a ground burst that close 
control on the height of the air burst was of 
relatively minor importance. This conclusion 
played an important part in the decision, made 
shortly before the close of World War II, to 
reduce the number of ring-type bomb fuzes in 
production from four to one. 

The difficulty of adequately treating this sub- 


SECRET 


BOMB FUZES 


221 


ject is further enhanced by some differences 
in military opinion on the usefulness of dif- 
ferent applications of the fuzes. For example, 
although in certain quarters it was concluded 
that the fuzes would be of little use in attacking 
well-entrenched positions, the fuzes were actu- 
ally used most frequently against antiaircraft 
positions, and the results reported by the users 
were, on the whole, very satisfactory. 

For the purposes of this report, the following 
general requirements are presented as adequate 
to specify fuzes that are useful under a rather 
wide variety of service conditions. 

Reliability. The fuzes should give, on the 
average, proper functions in excess of 70 per 
cent when release is made at any altitude from 
that required to ensure arming up to at least 
20,000 ft. This performance should hold for all 
train spacings in excess of a minimum deter- 
mined by a reasonable area of effectiveness of 
a single bomb of the train. 

Burst Heights. Under the conditions just 
stated, the great majority of proper functions 
should lie within the range 10 to 100 ft above 
the target area. This implies that the average 
height of proper functions should lie within 
the range 15 to 50 ft above the target area, 
regardless of release conditions within the 
limits stated above. 

Safety and Arming. The fuzes should be at 
least as safe to use as the safest of all other 
types of bomb fuzes. None should arm before 
traveling the minimum safe air travel [Min- 
SAT] specified for the particular type of fuze, 
and practically all should arm within ±10 per 
cent of the mean air travel to arming of the 
particular bomb-fuze combination under con- 
sideration. 

General Types 

As mentioned above (see Section 5.1.2) 
bomb fuzes may be divided into two major 
groups on the basis of the antenna system — the 
ring type and the bar type. Another type of 
classification is based on the r-f circuit. In this 
system, the classification depends upon whether 
detection is accomplished by a tuned diode de- 
tector [OD], by a reaction grid detector [RGD] 
or by a power-oscillating detector [POD] . This 
section will explain both types of classifica- 


tion and describe the general operational 
characteristics of each group. 

Ring and Bar. The external differences be- 
tween the ring and bar type are shown in Fig- 
ure 5, Chapter 1. The antenna system of the 
ring type consists of the ring of the fuze to- 
gether with the body of the bomb. This type of 
excitation is known as longitudinal excitation. 
The antenna of the bar type consists of the two 
bars on the fuze, and does not theoretically in- 
clude the bomb itself. Actually, there is usually 
some slight excitation of the bomb. This type 
of excitation is known as transverse. See table 
below for listing of fuzes of the two types. 

Bar-type fuzes may be expected to give better 
scores (less random functions) than most ring- 
type, for two reasons. (1) Since the vehicle is 
relatively unexcited in the bar type, any me- 
chanical disturbance, such as fin flutter, will 
affect the radiation only very slightly; and (2) 
bar-type fuzes have either RGD or POD cir- 
cuits, which, as will be shown later, are less 
susceptible to noise disturbances than the OD. 

One of the most marked differences between 
the two types is the much greater burst height 
possible with the bar type. This difference is 
due to the orientation of the radiation direc- 
tivity pattern, which differs by 90 degrees for 
the two types. For an antenna short compared 
with a wavelength, the maximum radiation is 
at an angle of approximately 90 degrees with 
the axis of the antenna, and the minimum along 
the axis. Since the antenna of the bar type is 
perpendicular to the axis of the bomb, the 
maximum radiation is along the bomb axis. 
Therefore, the bar-type fuzes have their maxi- 
mum sensitivity directly forward. Since for 
most release conditions the angle the bomb 
makes with the vertical is very small, this high 
forward sensitivity aids in the obtaining of 
large function heights. Ring fuzes, on the other 
hand, have their maximum radiation roughly 
perpendicular to the bomb axis and low radia- 
tion at the small angles encountered in level 
flight release from high altitudes. The ring 
fuzes are therefore sensitive to objects they 
pass while the bar fuzes are sensitive to objects 
directly ahead. As a result, bar fuzes give much 
higher heights for level-flight release conditions 
when the bomb is close to vertical. 


sec: 


222 


CATALOGUE OF FUZE TYPES 


Key to bomb fuzes 


Ring type 


Bar type 


Brown 

White 

Yellow 

White 

OD circuit 

RGD 

POD 

T-50-E1 

T-50-E4 

circuit 

circuit 

T-89 

T-90 

T-51 

T-82 

T-91 

T-92 

T-51-E1 (M-166) 

Series 

RGD circuit 

T-51-E2 


T-91-E1 (M-168) T-92-E1 

T-712 



R-F Circuit . The operational differences be- 
tween fuzes having the OD, RGD, or POD cir- 
cuits are less marked than those based on the 
antenna system, but they are significant. In gen- 
eral, better scores may be expected from RGD 
and POD than from OD circuits. The tuned 
diode detector circuit is much more sensitive to 
frequency modulation (usually produced by 
microphonics) than the RGD or POD circuits. 
Another factor influencing OD performance is 
tuning of the OD circuit, which is different on 
each bomb. Hence the diode circuit cannot be 
perfectly tuned on every vehicle. Since both r-f 
sensitivity and noise-response depend on tun- 
ing, there will be more spread in both height 
and scores for OD units on different vehicles 
than for RGD. 

The RGD circuit, therefore, is less suscep- 
tible to noise disturbances, particularly tube 
microphonics, than the OD and performs more 
uniformly on different vehicles. 

Specific Applications 

VT bomb fuzes may be divided into two cate- 
gories, depending upon mode of flight during 


release. Three fuzes, T-91, T-91-E1, and T-92 
were designed with short arming time (2,000 
to 2,600 ft MinSAT) specifically for dive bomb- 
ing and low-release altitude; all other fuzes 
(with 3,600 ft or greater MinSAT) for level 
flight release. 

Specific applications of these fuzes may be 
divided into two groups: (1) those depending 
upon the effect of the blast associated with the 
bomb burst, and (2) those depending upon the 
effectiveness of fragments from the bomb and 
its contents. In Table 5 (a) and (b) are of the 
first type and (c) through (f) the latter. The 
recommended type of fuze and most desirable 
burst height are given along with estimates of 
effectiveness as compared with similar use of 
a contact fuze. 

With the exception of the first and last appli- 
cations listed below, the M-166 and M-168 
fuzes may be regarded as adequate to meet all 
the applications listed. The M-166 is suitable 
when large burst heights are needed and the 
M-168 for low burst heights or for dive-bomb- 
ing applications. The earlier models have been 
listed merely for completeness. 


5 4.2 Functioning Characteristics 
Safety and Arming 

MinSAT s Available , Normal Arming. VT 
bomb fuzes have been designed with minimum 
safe air travels of 2,000, 2,600, 3,100, 3,600, 
4,500, and 8,000 ft. Of these MinSATs, how- 


Table 5. Applications of bomb fuzes. 



Application 

Burst 

height 

(ft) 

Estimated 

advantage 

Fuze 

a. 

Blast effect, M-56 

40-70 

1.5 to 2 

T-712 

b. 

Mine clearance by blast from Mk-44 

10-20 

Up to 2 

T-50 type 

c. 

General purpose (antipersonnel and light materiel) 

1. For 500- and 1,000-lb bombs 

20-70 

1 to 20 

T-90, T-50-E4, T-92* 


2. For bombs smaller than 500 lb and others up to 
2,000 lb 

20-70 

1 to 20 

M-166, M-168, T-50-E1, 


3. For all vehicles 

20-70 

1 to 20 

T-89, T-91 

M-166, T-51-E2 

d. 

Chemical warfare (gas) 

100-200 

4 to 7 

M-166, T-51-E2 

e. 

Fire bombing 

1. For 165-gal belly tank 

40-80 

2 

M-166, T-51-E2 


2. For M-10 spray tank 

5-15 

2? 

T-90, T-50-E4 


* The T-92 is listed last on account of inferior reliability (see Section 5.4.2). 


SECRET 


BOMB FUZES 


223 


ever, only three were used on fuze types reach- 
ing the production stage. These were : 

MinSAT Production type 

2,000 ft T-91, T-91-E1 (M-168) ; T-82-E2 

2.600 ft T-92 

3.600 ft T-50-E1, T-50-E4 ; T-51-E1 (M-166), T-51- 

E2; T-82-E1 ; T-89, T-90 

Data on the safe vertical drop and minimum 
release altitude corresponding to different 
MinSATs under various conditions are tabu- 
lated in reference 7. The types with 2,000-ft 
and 2,600-ft MinSATs were intended spe- 
cifically for dive-bombing applications. 

MinSATs Available, Delayed Arming. The 
air travel to arming on all the above types 
(except the T-82-E1) can be extended by the 
use of the device arming delay, air-travel, M-l 
(formerly T-2-E1), which will provide up to 
about 20,000 ft of additional air travel to arm- 
ing for any fuze adapted for holding it. The 
arming delay device is a wind-driven vane 
mechanism which is clamped on the fuze in 
such a way as to prevent rotation of the fuze 
arming vane (see Figure 1, Chapter 4). When 
the delay vane has rotated through a preset 
number of revolutions (manually adjustable in 
the field), the delay disengages itself from the 
fuze, allowing the fuze arming mechanism to 
operate in the normal fashion. The arming 
delay is constructed with a setting dial con- 
taining 25 divisions, each of which corresponds 
to about 800 ft of air travel on the M-30 test 
bomb. Data on arming delay settings under var- 
ious conditions are given in reference 7. 

Effect of Bomb Size on Air Travel. For a 
given rotor setting the air travel to arming 
generally increases with the bomb size. This 
effect is due to the additional obstruction 
offered by the larger bomb nose to the flow of 
air past the vanes. The relative air travel for 
different vane types on various vehicles is as 
follows : 


Vane 


Bomb 


Metal 

M-30 

M-81 

M-64 

and 

100-lb GP 

260-lb frag 

500-lb GP 

plastic 

1.00 

1.02 

1.15 

Vane 


Bomb 


Metal 

M-65 

M-66 

M-56 

and 

1,000-lb GP 

2,000-lb GP 

4,000-lb GP 

plastic 

1.32 

1.58 

1.48 


Safety Pin. Booster cups on the production- 


type fuze models, with the exception of 
T-50-E1, T-50-E4, and T-51-E2, are equipped 
with a safety pin for indicating that the fuzes 
are safe for handling. The pin locks the arming 
mechanism and can be inserted only if the det- 
onator rotor is in the unarmed position. Fuzes 
are issued with the safety pin in place and can- 
not be installed in the fuze-well unless the pin 
is removed. 

Reliability 

With few exceptions, ring-type fuzes released 
under standard test conditions (from 10,000 ft 
at 200 mph), can be expected to give uniform 
performance of about 75 to 80 per cent proper 
functions. The M-168 fuzes should give con- 
sistently better scores (about 90 per cent 
proper). The performance of T-92 fuzes was 
not satisfactory (an average of only 58 per 
cent proper functions was obtained in experi- 
mental and acceptance tests). A possible ex- 
planation for the increased incidence of early 
functions may be found in the fact that the 
T-92’s were built with broader pass-band am- 
plifiers and were more sensitive than the other 
fuzes. The fuze appeared to be unduly suscep- 
tible to certain structural variations in stand- 
ard bombs. The effect of fin thickness on fuze 
performance is discussed in Chapter 9. 

Fuze performance is dependent to some ex- 
tent upon altitude of release. Scores will gen- 
erally be slightly poorer for release altitudes 
above 10,000 ft than under standard release 
conditions; on the other hand, performance 
can be expected to improve somewhat with 
lower release altitudes. 

Bar-type fuzes, on the whole, should give 
better performance than ring-type fuzes, ex- 
cept the M-168. Under standard release condi- 
tions, proper function scores of T-51 and T-82 
type fuzes should fall close to an average of 90 
per cent. 

The possibility of sympathetic functioning 
must be considered when proximity fuzes with- 
out arming delays are released in train. If the 
spacing between bombs is too small, one armed 
fuze may react upon the random burst of an- 
other. The train spacing should exceed 50 ft 
on the ground for small bombs (less than 500 
lb), and should exceed 100 ft for large bombs. 


224 


CATALOGUE OF FUZE TYPES 


Train spacing is unimportant if arming delays 
are used because the delays postpone arming 
until the bombs are widely spaced. 8 These de- 
vices can be used on most models (see Section 
5.4.2). 

Burst Heights 

Burst heights of VT bomb fuzes are affected 
by a number of factors external to the fuze, 
such as vehicle, altitude of release, plane speed, 
and target factor. 

Ring Type. Proper function heights of ring- 
type fuzes under standard test conditions (i.e., 
dropped over water from 10,000 ft at 200 mph) 
can be expected to lie between 10 to 100 ft, with 
average heights ranging from 15 to 50 ft. Satis- 
factory uniformity of burst heights in the same 
range should be obtained for fuze-vehicle com- 
binations recommended in the fuze data sheets 
below. Lower function heights will result from 
the mismatching of vehicle and fuze. The effect 
of release altitude upon burst height is not 
simply defined. For some fuzes, such as the 
T-89, averages of proper function heights can 
be expected to increase with increasing alti- 
tudes of release; for other fuzes, the reverse is 
true (see Figures 9 and 21). 

Bar Type. The forward sensitivity pattern 
of bar-type fuzes causes much higher burst 
heights than those obtained with the ring-type 
fuze. Function heights as high as 240 ft above 
water are considered proper for T-51 and T-82 
type fuzes, released under standard conditions. 
Average function heights of 50 to 100 ft over 
land can be expected from either fuze mounted 
on M-81. Theoretically, performance of bar- 
type fuzes should be nearly independent of 
vehicle; however, lower burst heights will be 
produced by fuzes mounted on 500-lb bombs 
and larger (with the exception of the T-51 on 
M-56) than by fuzes mounted on 100- to 260-lb 
bombs. For burst heights of bar-type fuzes on 
various bombs relative to burst heights on 
M-81, see Table 14. 

343 Structure 

General Arrangement 

The general layout of all bomb fuzes (except 
the T-82 series) is illustrated in Figure 17, 


Chapter 4. Except for the much larger an- 
tennas (ring or dipole bars) and the introduc- 
tion of an axially located drive shaft running 
from the vane through the electronic system, 
the front section is practically identical with 
that of the Army rocket fuzes T-5 and T-6. The 
battery of the T-5 is replaced by a magneto- 
type generator, a gear-reduction system, and 
most of the components of a rectifier-filter sys- 
tem for the generator, all in about two-thirds 
of the fuze length required for a battery. At 
this level, the fuze housing is shouldered in to 
seat on the nose of the bomb. The narrower 
extension of the housing contains a cylindrical 
filter and firing condenser, through the center 
of which runs a slow-speed shaft from the gear- 
reduction system to the terminal elements of 
the arming mechanism. The housing is closed 
at the rear end by a threaded cup containing 
a booster charge of tetryl. 

All bomb fuzes are shipped completely 
assembled and loaded and require no field test- 
ing or assembly operations such as those re- 
quired with the battery-powered T-5 and T-6. 

Arming Mechanism 

The principal elements of the arming mech- 
anism of all bomb fuzes (except the T-82 
series) are shown in Figure 20, Chapter 4. A 
worm-gear train drives a slow-speed shaft to 
which is keyed a Bakelite detonator rotor by 
means of a spring-loaded transfer pin. The 
detonator rotor carries an electric detonator, 
eccentrically located in a hole as shown in the 
rear-end view, Figure 24, Chapter 4. The rotor 
rides in a Bakelite housing which is mounted 
on the rear end of the rectifier filter assembly 
shown in Figure 27, Chapter 4. This housing 
serves two purposes : it has a slot that permits 
the spring-loaded transfer pin to leave the slot 
in the slow-speed shaft after the rotor has 
turned a predetermined angle, thus locking the 
rotor in the armed position; it carries electric 
contact springs that complete the detonator 
circuit immediately before the rotor is locked in 
place. In the unarmed position, the tetryl 
booster charge is protected from the detonator 
by a thick brass safety plate. This plate carries 
a tetryl plug to which the detonator is juxta- 
posed in the armed position. 


BOMB FUZES 


225 


All bomb fuzes are provided with a vane- 
locking pin, or equivalent device, from which 
is withdrawn an arming wire when the bomb is 
dropped (see Figure 20, Chapter 4). 

A safeguard that was necessary on the 
earlier models was the closed slot on the slow- 
speed shaft. In order to prevent assembly with 
an incorrect rotor setting, the keyway is not 
extended to the end of the slow-speed shaft. 
The rotor housing is notched at the proper 
angle from the armed position, and the transfer 
pin can be pressed into the keyway of the slow- 
speed shaft only when this keyway is aligned 
with the notch. An incorrect setting can be 
obtained in these models only by rotation of the 
vane, the locking pin of which was sealed in 
place before assembly. 

This safeguard was unnecessary in the later 
models, which are provided with a safety pin 
(see Figures 23 and 24, Chapter 4) which 
can be inserted into and withdrawn at will 
from the completely assembled fuze only if the 
detonator rotor is in the correct position. 

The data sheets (see Section 5.5) tell which 
of these additional safety features appear in 
each of the production model fuzes. The possi- 
bility of using the arming delay device is also 
indicated in Section 5.5. The purpose and 
method of using this auxiliary device has 
already been outlined in Section 5.4.2 above. 
Its construction and operation can be readily 
visualized from Figure 1, Chapter 4. 

R-F System 

Oscillator-Diode [ OD ] Circuits. The OD cir- 
cuit used in bomb fuzes is nearly the same as 
that used in the Army rocket fuzes T-5 and T-6 
(see Figure 2). In the bomb-fuze diode circuit, 
R5 is connected to the other side of C4 instead 
of to ground. No switches are used in the A and 
B supply lines, the resistance in the diode fila- 
ment line is increased to 10 ohms, and the ca- 
pacity of the by-pass condensers C2, C5, and 
C6, is increased to 150 ppf each. Another 150- 
|i|if by-pass from the B supply line to ground 
is located in the amplifier section of the fuze. 

The Reaction-Grid-Detector [ RGD ] Circuit. 
The RGD circuit is used in the M-168 and the 
T-92-E1 ring-type bomb fuzes (see Figure 5). 
Component values are given in Table 6. 


Table 6. Component values for RGD oscillator 
in M-168 and T-92-E1 fuzes.* 



Value 


Value 

Resistor 

(ohms) 

Condenser 

(w*f) 

R1 

100,000 

Cl 

5 

R2 

47,000 

C2 

30 

R3 

2,200 

C3 

30 



C4 

5 



C6 

150 



C22 

150 


Triode : 

: NR3A 


* Ll and L2 

are adjusted to obtain required frequency and sen- 

sitivity. C22 is 

located in the amplifier section. 


The RGD oscillator used in the M-166 bar- 
type bomb fuze is shown in Figure 6. Values of 

components are given in Table 7. 


Table 7. 

Component values of RGD 

oscillator 

in M-166 fuze.* 




Value 


Value 

Resistor 

(ohms) 

Condenser 

(wrf) 

R1 

1,000 

Cl 

25 

R2 

3 

C2 

50 

R3 

33,000 



R4 

47,000 




Triode 

: NR3A 



* Ll : oscillator and antenna coils wound on same core. L2 : r-f 
choke. 



Figure 5. Reaction-grid-detector circuit used in 
M-168 and T-92-E1 bomb fuzes. 


Oscillator Assemblies. With the exception of 
the T-82, the physical layout of the oscillators 
in all bomb fuzes is nearly the same. The 
mounted components and their circuital rela- 
tionships are illustrated in Figures 13, 14, and 
15, Chapter 3. Phenolic (thermosetting) 
mounting blocks (Figure 5, Chapter 6) were 
used in all except the M-166, in which a sty- 


SECRET 


226 


CATALOGUE OF FUZE TYPES 


ramie (thermoplastic) block was used (Figure 
6, Chapter 6). 

Amplifier 

Circuits in Ring-Type Fuzes. The basic am- 
plifier circuit of all ring-type bomb fuzes is 
shown in Figure 26, Chapter 3. Table 8 pro- 


Table 8. Component values for amplifier No. 11 
in T-50-E4 fuze.* 


Resistor 

Value 

(megohms) 

Condenser 

Value 

<w*f) 

R7 

0.68 

C7 

5,000 

R9 

5.6 

C8 

3-20 

RIO 

1.0 

CIO 

5,000 

Rll 

1.5 

Cll 

500 

R12 

0.47 

C12 

200 

R13 

2.2 

C13 

200 

R14 

6.8 

C14 

1,000 

R15 

2.2 

C15 

500 

R19 

3 ohms 

C16 

50 

R21 

6.8 ohms 



R30 

1.0 




Pentode : 

NS-5 



Thyratron 

: NS-4 



* C16 is optional; may be connected between ground or filament 
and any part of the input circuit to minimize r-f effects. Additional 
items in amplifier section: a test lead brought out from the thyratron 
grid; 150-.u/u£ by-pass condenser from B+ to ground. 

vides the component values for the No. 11 am- 
plifier of the T-50-E4 and notes on minor dif- 
ferences from the circuit shown in the figure. 
Table 9 shows the differences that occur in 
other amplifiers of this series. 



Figure 6. Reaction-grid-detector circuit used in 
M-166 bomb fuze. 


Circuit in Bar-Type Fuze. The basic amplifier 
circuit of the M-166 (T-51-E1) bar-type bomb 


fuze is shown in Figure 30, Chapter 3, for 
which Table 10 provides the component values. 


Table 

9. Variations from 

amplifier 

No. 11 

(T-50-E4) in other ring- type bomb fuzes. 

Fuze 

T-50-E1 

T-91 




T-89 

M-168 

T-92 

T-92-E1 

Amplifier 

No. 10 

No. 20 

No. 16 

No. 18 

Resistor 





(values 





in meg- 
ohms) 
Rll 


* 


1.68* 

R12 

Condenser 

0.82 

1.5* 

0.82 

0.68* 

(values 
in /ifi f ) 

C7 

10,000 



2,000 

C8 

5-20 

0-20 


0-20 

CIO 

20,000 

20,000 


20,000 

Cll 


200 


200 

C12 


500 


500$ 

C13 

500 

500 


500 

C14 

2,000 



2,000 

C15 



300$ 

200§ 


* Adjust to obtain required frequency. 

f Feedback loop connection is shifted from pentode plate to the 
thyratron grid side of C14. 

t A 200-fifif condenser is connected from the input line to ground. 
§ Feedback loop resistors Rll and R12 connected to center point 
between the legs of pentode filament by two 1,000-ohm resistors. 


Table 10. Component values for amplifier in 
M-166 (T-51-E1) fuze.* 


Resistor 

Value 

(megohms) Condenser 

Value 

<W*f) 

R2 

3 ohms 



R5 

0.39 

C3 

0.005 

R6 

1.0 

C4 

50 nni 

R7 

0.47 

C5 

0.01 

R8 

1.0 

C6 

0.0002 

R9 

5.6 

C7 

0.0004 

R10 

2.2 

C8 

0-20 w f 

Rll 

3 ohms 




Pentode: NS-5, NR-5 or 

NGE-5 


Thyratron : 

NS-4 


* Not shown 

in Figure 30, 

Chapter 3: A 

test lead brought out 


from the thyratron grid; each side of the A supply line is grounded 
(in the oscillator section) by a 3-ohm resistor shunted by a 50-^f 
by-pass condenser. 

Amplifier Assemblies. A number of different 
types of amplifier assemblies are found in the 
bomb fuzes. These are illustrated in the follow- 
ing figures in Chapter 6 : Figure 17, right, for 
Philco models; Figure 17, left, for Emerson 
models (both are disk variations of the sand- 
wich type of assembly) ; Figure 14 for the 
Zenith M-166 (“dog collar” type of assembly). 


PRODUCTION FUZE DATA SHEETS 


227 


For reasons discussed in Chapter 6, the type of 
assembly used is, generally speaking, a charac- 
teristic of the manufacturer rather than of the 
fuze, and a more detailed description is unwar- 
ranted here. 

In all bomb fuzes, the thyratron is included 
in the amplifier assembly. Tung oil was used as 
a potting material for the amplifier assemblies, 
except for late Emerson production, for which 
Glidden potting compound was used. 

Power Supply and Firing Circuit 

The power supply and firing circuit used in 
bomb fuzes is shown in Figures 75 and 76, 
Chapter 3. The lead from the thyratron plate 
[TP] tap is connected to one of the spring con- 
tacts in the detonator rotor housing; the other 
spring contact is connected to B+ and through 
the firing condenser C20 to ground. The filter 
condenser is C19, and C18 is the voltage regula- 
tion condenser. 


55 PRODUCTION FUZE DATA SHEETS 
5,51 Scope 

The following set of data sheets covers infor- 
mation, where available or pertinent, for pro- 
duction fuzes only, in the following order : 

Item 1. Tabulations of arming, electrical, 
and performance data. 

Item 2. Curves of burst-height performance. 

Item 3. Amplifier gain curves. 

Item 4. Radiation patterns and loading 
curves. 

The T-51-E2 has been omitted, since it repre- 
sents only about 4 per cent of the total bar-type 
production and its characteristics were prac- 
tically the same as those of the Zenith M-166, 
except that it lacked the safety pin. 

The T-712, although produced on an even 
smaller scale than the T-51-E2, has been in- 
cluded because certain of its characteristics are 
quite different from those of other bar-type 
fuzes. It is understood that its production was 
limited on account of the limited supply of M-56 
bombs. 

Coverage in this section has been limited to 
production items because these are the only 


fuzes which are in stock in appreciable quanti- 
ties. 

Explanatory Notes 

Item 1. 

(a) In the tabular data , entries are omitted 
if all in a row are repetitions of that in the 
first column. 

(b) Electrical data represents overall produc- 
tion averages as shown on CTL Quality Control 
Charts, where available. 

For longitudinally excited fuzes, the maxi- 
mum sensitivity is given ; the approximate load 
resistance R (in 10 3 ohms) at which maximum 
sensitivity occurs appears in parentheses after 
the sensitivity value. For OD circuit fuzes, the 
sensitivity S' at any other load R' can be calcu- 
lated with sufficient accuracy from the formula 
S' 4 RR f 

S (R + R'f 

For the RGD circuit, this formula is less accu- 
rate, and loading curves are given where avail- 
able. 

The laboratory data on detuning apply to OD 
circuit fuzes as tested with a standard load 
approximately equivalent to that presented by 
the missile for which the fuze was designed. 
For bomb fuzes, the bombs represented in the 
laboratory tests were M-30 for Brown fre- 
quency and M-64 for White. For information 
concerning the effect of detuning on sensitivity, 
see Section 2.7. 

Effective critical voltages are the maxima 
obtained in the detuning tests. 

(c) Function scores are averaged without 
regard to reflection coefficient or plane speed 
but are restricted to missiles, as stated in 
Table 11. The very few late functions are in- 
cluded with the proper functions. 

Function heights are for release from 10,000 
ft at a plane speed of 200 mph over water with 
a reflection coefficient of approximately 0.81, 
unless otherwise indicated by footnote. Part of 
the original data were obtained under other 
conditions. The method of reduction to a com- 
mon condition is covered in Section 9.4. 

(d) Under production , the quantities given 
are the approximate number of metal parts 
(MP) lots produced, usually about 1,000 units 
per lot. 



228 


CATALOGUE OF FUZE TYPES 


(e) The AN/CPQ-( ) designation system 
was originally set up to distinguish between 
vane leads, arming distances, rotor settings, 
etc., in different metal parts assemblies as de- 
livered from the factory. Later it became neces- 
sary to make changes in the rotor settings in 
assembling some of the metal parts products 
into complete fuzes at Picatinny Arsenal, so 
that the AN/CPQ designations lost their sig- 
nificance in some cases. However, since this 
nomenclature was used almost exclusively in 
the many reports of the Control Testing Lab- 
oratory at the National Bureau of Standards, 
it has been recorded here as an aid to anyone 
who has occasion to study the laboratory per- 
formance of production models. The lack of a 
complete 1-to-l correspondence between metal 
parts designations and fuze (T- or M-) desig- 
nations is unavoidable. 

Item 3. The PkAF and peak gain as appear- 
ing on the curves are not always consistent 
with the audio-frequency at peak amplification 
[PkAF] and millivolts to fire [MvF] at peak 
given in the tabular data, because considerably 
smaller samples were used in determining the 


amplifier characteristics. The curves can be 
relied upon for shape but should be adjusted 
for location of peak. 

Item U- Only those radiation patterns that 
are most likely to be useful in the calculation of 
burst heights have been included; for other 
patterns and much useful additional data for 
this purpose, see reference 3. 

Abbreviations. 

MinSAT: Minimum safe air travel, dur- 
ing which no fuzes will arm. 

CF: Carrier frequency of the fuze trans- 
mitter. 

S: Sensitivity, as defined in Section 3.1.2. 
Amp. No. : Signal Corps identification 
number of amplifier. 

PkAF: Audio-frequency at peak amplifi- 
cation. 

MvF: Millivolts to fire (the thyratron) 
applied at amplifier input. 

CV : C-bias voltage on the thyratron. 
EC: Effective critical voltage, at which 
bias voltage the thyratron fires. 

Rel gain : Relative gain of the amplifier. 
SD time: Self-destruction time. 


Data Common to Production VT Bomb Fuzes 

Table 11 . General purpose models. 


Fuzes 


Ring-type Bar-type 



Brown 

White 


Property 

T-50-E1, T-89, T-91, 
T-91-E1 (M-168) 

T-50-E4, T-90, T-92 

T-51-E1 (M-166) 

Physical characteristics: 

Overall length (in.) 

10t? 

10^2 

10^2 

Length from shoulder (in.) 

4H 

4M 

4M 

Overall width (in.) 

3f 

3f 

10 

Weight (lb) 

4 

4 

4 

Vane speed range* (1,000 rpm) 

15-30 

15-30 

20-35 

Proof test conditions: 

Bomb 

00 

00 

i 

00 

£ 

M-64 

M-57, -81, -88 

Release alt. (ft) 

10,000 

10,000 

10,000 

Uses: 

Physically interchangeable with contact fuze 

M-103 

M-103 

M-103 

Some bombs for which the fuzes are useful 

GP: M-30, -57, -66 
Frag: M-81, -88 

GP: M-64, -65 

GP: M-30, -57, -64, 
-65, -66 

Frag: M-81, -88 


* Laboratory test speed range. 


PRODUCTION FUZE DATA SHEETS 


229 


5.5.2 

Bomb Fuzes, Ring Type, Brown Carrier 

Table 12. Characteristics and scores. 




M-168 

(T-91-E1) 

Level or dive release 

T-91 


Level release 

T-89 T-50-E1 

Arming 

MinSAT (ft) 

2,000 

2,000 

2,000 

3,600 

3,600 

Safety pin 

Yes 

Yes 

Yes 

Yes 

No 

Delay device 

Yes 

Yes 

Yes 

Yes 

Yes* 

Rotor setting (°) 

65 

65 

65 

110 

100 

Rotor shaft 

Open 

Closed 

Closed 

Closed 

Closed 

Vane 

10-blade metal prop 




Vane angle (°) 

55 





Electrical 

Radio 

Circuit 

RGD 

OD 

OD 

OD 

OD 

CF 

+0.9 

-1.5 

+ 1.1 

-1.5 

— 1.5f 

S (volt) 

30 (5) 

16 (5.5) 

18 (5.5) 

16.5 (5.5) 

16.5 (5.5) 

Detuned (%) 


3 

4 

4 

4 

Audio 

Amp. No. 

20 

20 

20 

10 

10 

PkAF (c) 

93 

94 

97 

116 

116 

MvF (Pk) 

23 

25 

25 

26 

26 

CV (-volt) 

7.7 

8.2 

7.6 

8.4 

8.4 

EC 

3.8 

4.9 

4.3 

4.8 

4.8 

Proof performance 

Burst height (ft) 

50 

37 

44 

35 

35 

Proper (%) 

92 

87 

84 

83 

83 

Random (%) 

7 

11 

10 

13 

13 

Dud (%) 

1 

2 

6 

4 

4 1 

Production 

Manufacturer 

Emerson 

Philco 

GE 

Philco 

Philco 

Quantity (MP lots) 
AN/CPQ- 

27 

2C 

70 

50 

10 

130 

PA- 

329 

307 

307 

263 

180 


* Not loaded with fuzes, f First 50 MP lots manufactured at + 2, excluded from average. + 19% dud on first sample tests of the 
first 42 lots, due to faulty rotor contact spring adjustment. Not included in average. 



LOAD RESISTANCE, R A (I0 3 0HMS) 


Figure 7. Oscillator loading characteristics of 
M-168 bomb fuze. Plate current I Vy grid voltage 
Eg , and radiation sensitivity 5 are shown as 
functions of radiation resistance R a . 



Figure 8. Amplifier gain as function of signal 
frequency for ring-type Brown-carrier bomb fuzes. 


SECRET 




RELEASE ALTITUDE (10 FT) M ^ _ RELEASE ALTITUDE (10 FT) 


230 


CATALOGUE OF FUZE TYPES 


20 

18 

16 

14 

12 

10 

8 

6 

4 

2 



200 250 300 350 400 

PLANE SPEED (M PH) 


?IGUR1 
? or M 
'eflect 


E 9. Iso-burst-height curves (predicted) 
-168 fuze on M-64 (500-lb) GP bomb for 
ion coefficient of 0.5. 



200 250 300 350 400 


PLANE SPEED (M PH) 

Figure 11. Iso-burst-height curves (predicted) 
for M-168 fuze on M-81 (260-lb) fragmentation 
bomb for reflection coefficient of 0.5. 



Figure 10. Iso-burst-height curves (predicted) 
for T-50-E1 or T-89 fuze on M-81 (260-lb) frag- 
mentation bomb for reflection coefficient of 0.5. 



Figure 12. Cumulative distribution of indi- 
vidual burst heights for various ring-type Brown- 
carrier fuzes on M-81 (260-lb) fragmentation 
bomb. Reflection coefficient is 0.8 except as noted. 
A, T-50-E1 and T-89; B, Philco T-91, reflection 
coefficient 0.6; C, GE T-91; D, M-168, reflection 
coefficient 0.6, plane speed 240 mph. 


PRODUCTION FUZE DATA SHEETS 


231 



Figure 13. Radiation directivity pattern for 
Brown frequency longitudinal end excitation of 
bombs: A, M-30 or M-81 (V 2 wp = 0.124); B, 

M -66 (% irp = 0.207). 



0 (DEGREES) 


Figure 14. Small angle detail for M-30 pattern 
of Figure 13 for frequencies: A, B — 1; B, 
B + 5.5. 



2 4 6 8 10 12 14 16 18 20 

0( DEGREES) 


Figure 15. Small-angle detail for M-81 pattern 
of Figure 13 for frequencies: A, B + 0; B, 
B + 9.4. 



0 2 4 6 8 10 12 14 16 16 


0 (DEGREES) 

Figure 16. Small-angle detail for M-66 pattern 
of Figure 13 for frequencies: A, B + 5.5; B, 
B — 0.8. 


CRE 


232 


CATALOGUE OF FUZE TYPES 


Bomb Fuzes, Ring Type, White Carrier 

Table 13. Characteristics and scores. 


Level release Dive release 

T-90 T-50-E4 T-92 T-92-E1 


Arming 

MinSAT (ft) 

Safety pin 
Delay device 
Rotor setting 0 
Rotor shaft 
Vane 

Vane lead (in.) 
Electrical 
Radio 
Circuit 
CF 

S (volt) 

Detuned (%) 
Audio 
Amp. No. 

PkAF (c) 

MvF (Pk) 

CV (—volt) 

EC (-volt) 

Proof performance 
Burst height (ft) 
Proper (%) 
Random (%) 

Dud (%) 
Production 
Manufacturer 
Quantity (MP lots) 
AN/CPQ- 
PA- 


3,600 

3,600 

Yes 

No 

Yes 

Yes* 

145 

140 

Closed 

Closed 

3-blade Bakelite prop 


9 


OD 

. OD 

+9.0 

+9.3 

19 (6.5) 

18 (6.5) 

5 

5 

11 

11 

190 

185 

27 

30 

7.4 

7.4 

4.6 

4.6 

39 

39 

78 

78 

19 

19 

3 

3 

Emerson 



50 

80 

IB 

1C 

264 

181 


2,600 

2,600 

Yes 

Yes 

Yes 

Yes 

110 

80 

Closed 

Open 


OD 

RGD 

+8.5 

+5.6 

18 (6.5) 

30 (3.5) 

4 


16 

18 

160 

156 

22 

21 

7.4 

7.6 

4.6 

4.0 

33 

40 

58 

79 

31 

18 

8 

3 

44 

6 

1A, IB 

1A, IB 

306 



* Not loaded with fuzes. Requires mounting bracket as on T-51. 



Figure 17. Cumulative distribution of individual 
burst heights for ring-type White-carrier fuzes 
on M-64 500-lb GP bomb. Reflection coefficient 
is 0.8. 



Figure 18. Amplifier gain as function of signal 
frequency for ring-type White-carrier bomb 
fuzes. Amp 11 in T-50-E4, Amp 16 in T-92, Amp 
18 in T-92-E1. 


(eu- 


PRODUCTION FUZE DATA SHEETS 


233 



Figure 19. Radiation directivity patterns for 
White + 10 frequency longitudinal end excitation 
of bombs : A, M-64 ( V 2 tt/3 = 0.208) ; B, M-65 
(y 2 tt/3 = 0.182). 



O 2 4 6 8 10 12 14 16 18 20 

6 (0EGREES) 


Figure 20. Small-angle detail for Figure 19: 
A, M-65 at W + 10; B, M-65 at W + 0.2; C, 
M-64 at W + 10; D, M-64 at W + 0.2. 



200 250 300 350 400 


PLANE SPEED (M P H) 

Figure 21. Iso-burst-height curves (predicted) 
for T-50-E4 or T-90 fuze on M-64 (500-lb) GP 
bomb for reflection coefficient of 0.5. 


SECRET 


234 


CATALOGUE OF FUZE TYPES 



Figure 22. Oscillator loading characteristics of the T-92-E1 bomb fuze. Plate current I P , grid voltage 
Eg, and radiation sensitivity S are shown as functions of radiation resistance R a . 

Bomb Fuzes, Bar Type, Yellow Carrier 

Table 14. Characteristics and scores. 

Level or dive release Special for M-56 GP 

M-166 (T-51-E1) T-712 


Arming 

MinSAT (ft) 

Safety pin 
Delay device 
Rotor setting (°) 
Rotor shaft 
Vane 

Vane lead (in.) 
Electrical 
Radio 
Circuit 
CF 

S (volt) 

Audio 
Amp. No. 

MvF (165 c) 

MvF (300 c) 

EC (-volt) 

CV (-volt) 

Proof performance 
Burst height 
Proper (%) 
Random (%) 

Dud (%) 
Production 
Manufacturer 
Quantity (MP lots) 
AN/CPQ- 
PA- 


3,600 

Yes 

Yes 

153 

Closed 

3-blade Bakelite prop 
6 


RGD 


8.5 

7.4 

9.9 

14 

13 

11 

P5 



32 

33 

52 

42 

46 

74 

3.7 

3.8 

3.6 

7.9 

7.8 

7.8 



% 

110 

110 

50* 

91 

85 

100 

9 

15 

0 

0 

0 

0 

Zenith 

Emerson 

Zenith 

230 

24 

2 

5C 



283 

283 



♦Tested on M-81 (reflection coefficient, 0.6; speed: 240 mph). 


PRODUCTION FUZE DATA SHEETS 


235 


Bomb weights and relative burst heights for M-166. 


Bomb 

Weight 

(lb) 

Relative 

burst 

height 

Bomb 

Weight 

(lb) 

Relative 

burst 

height 

M-30 

100 

1.28 

M-64 

500 

0.73 

M-88 

220 

1.00 

M-65 

1,000 

0.69 

M-81 

260 

1.00 

M-66 

2,000 

0.40 

M-57 

250 

1.00 

M-56 

4,000 

1.37 




Figure 25. Amplifier gain as function of signal 
frequency for bar-type Yellow-carrier bomb 
fuzes. 


Figure 23. Burst height as function of altitude 
of release for Zenith T-51-E1 fuze on several 
bombs. Reflection coefficient is 0.8. 


Navy Rocket Fuze, Ring Type, 
Brown Carrier 



Figure 24. Cumulative distribution of individual 
burst heights for Zenith T-51-E1 fuze on M-81 
(260-lb) fragmentation bomb. Reflection coeffi- 
cient is 0.6. 


Table 15. Characteristics and scores. 



Plane to Surface 
T-2004 

Arming 

MinSAT (ft) 

1,000 

Safety pin 

Yes 

Vane 

10-blade metal prop 

Vane angle (°) 

65 

Electrical 

Radio 

Circuit 

OD 

CF 

+ 1.3 

S (volt) 

15 

Detuned (%) 

2 

Audio 

PkAF (c) 

125 

MvF (Pk) 

109 

CV (-volt) 

7.7 

EC (-volt) 

4.1 

Proof performance 

Burst height* 

30 

Reflection coefficient 

0.81 

Proper (%) 

94 

Random (%) 

3 

Dud (%) 

3 

Production 

Manufacturer 

Philco 

Quantity (MP lots) 

75 

MP designation 

AN/CPQ-3A 

PA- 

315 


* Fired from a ground launcher at approximately 30-degree eleva- 
tion. External physical dimensions are same as those of ring-type 
bomb fuzes. 


SECRET 



236 


CATALOGUE OF FUZE TYPES 


HORIZONTAL FLIGHT- RELEASE ALTITUDE (FT) 



1 
CL 

2 


LlI 

V) 

< 

Ui 


300 


00 UJ 

♦ H 

2 ?°5 



30°DIVE ANGLE 


HORIZONTAL FLIGHT-RELEASE ALTITUDE (FT) x 



45° DIVE ANGLE 


HORIZONTAL FLIGHT-RELEASE ALTITUDE (FT) 



UJ 

300 £ 


250 


Figure 26. Equivalent altitude and plane speeds for level-flight and dive-bombing releases at dive 
angles of 30°, 45°, and 60°. Given burst height as function of level-flight release altitude and plane speed 
(see, for example, iso-burst-height curves), this chart may be used to determine burst height for dive- 
bombing releases. Scale for M-64 bomb may be used for larger bombs in GP series. Scale for M-81 bomb 
gives rough approximation for M-30. 



PRODUCTION FUZE DATA SHEETS 


237 



O 10 20 30 40 50 60 70 

DIVE ANGLE 


Figure 27. Burst height as function of dive 
angle for T-2004 fuze on 5.0-in. AR Navy rocket 
for firing at plane speed of 300 knots at range of 
1,500 to 2,000 yd. (Fired over ground at 
Inyokern.) 



Figure 28. Cumulative distribution of indi- 
vidual burst heights for T-2004 fuze on 5.0-in. 
AR Navy rocket for firing at plane speed of 300 
knots at range of 1,500 to 2,000 yd (Inyokern 
data). 



Figure 29. Amplifier gain as function of signal 
frequency for the T-2004 ring-type Brown-car- 
rier Navy rocket fuze. 





Figure 30. Radiation directivity pattern for 
Brown frequency longitudinal end excitation of 
5.0-in. AR Navy rocket (Vz wp = 0.130). 



238 


CATALOGUE OF FUZE TYPES 


Army Rocket Fuzes 

Table 16. Characteristics and scores. 


Type: longitudinally excited. Carrier: Red, Yellow, Green. 
T-5: Plane- to-plane or plane- to-ground 
T-6: Ground-to-ground 

Arming: MinSAT (ft) T-5: 525 

T-6: 2,400 

Electrical (same for T-5 and T-6) 

(volt): 18. 

Test Voltages 




A: 1.40 

A: 1.15 



B: 135 

B: 115 

PkAF (c) 


121 


MvF (Pk) 


37 

51 

Rel gain at 20 c (%) 


18 

22 

Rel gain at 300 c (%) 


19 

25 

SD time (sec) 


8 


Proof performance 


T-6 



T-5 

Philco 

A 

Friez 

Proper (%) 

81 

84 

72 

Early (%) 

13 



Late or Mid (%) 

2 

12 

24 

Dud (%) 

4 

4 

4 


Weight and dimensions (same for T-5 and T-6) 

Length (overall): 7^ in. Length (outside rocket): 2^ in. 
Width (overall): 3^ in. Weight (lb): 2f 
Physically interchangeable with contact fuze PD-M-4 

West- 

Manufacturers Emer- ing- 

son Friez GE Philco house All 

Quantity (MP lots) 100 25 80 1 10 80 395 


T-5 ON ROCKET T-22 


(EGLIN FIELD ST 2-45-16) 



Figure 32. Burst height as function of dive 
angle for T-5 fuze on T-22 Army rocket for fir- 
ing at plane speed of approximately 300 mph at 
range 700 to 1,000 yd. (Fired over ground at 
Eglin Field.) 


Circuit: OD. Sensitivity 



Figure 31. Cumulative distribution of indi- 
vidual burst heights for T-6 fuze on 4.5-in. Army 
rocket for several firing elevations as indicated. 
Reflection coefficient is 0.96. 



Figure 33. Radiation directivity pattern for 
Red and Green frequency longitudinal end ex- 
citation of 4.5-in. Army rocket. 


SECRET 


PREPRODUCTION FUZES 


239 



Figure 34. Amplifier gain as function of signal 
frequency for the T-5 or T-6 Army rocket fuze. 


PREPRODUCTION FUZES 


The VT fuzes which were not in production 
at the end of World War II are covered in this 
section. They were as follows : 


Vehicle 

Fuze 

Type 

Frequency 

Bomb 

T-82 

Bar 

White 

Navy rocket 

T-30 

Ring 

Brown 


T-2005 

Longitudinally 

excited 

Brown 

Mortar shell 

T-132 

Longitudinally 

excited 

White 


T-171 

Longitudinally 

excited 

Brown 


T-172 

Transversely 

excited 

Yellow 


5 61 Bomb Fuze T-82, Bar Type, 

White Frequency 

The bomb fuze T-82 was designed for the 
same purposes as the M-166 (T-51-E1). When 
it was found that the M-166 would meet mili- 
tary requirements adequately and could be pro- 
duced in quantity with a minimum of new 
tooling, the need for the T-82 diminished and it 
did not reach the production stage until just 
before the end of World War II. The data given 
here were obtained from pilot-production 
samples and from the mass-production type- 
approval sample. 

The T-82 featured a turbine-driven generator 
mounted in the base of the fuze. An air intake 
port was provided through the center of the 


fuze; there were two exit ports on opposite 
sides of the fuze near the base (see Figure 28 
of Chapter 4). The design had several advan- 
tages over that of the other bomb fuzes. The 
location of all moving parts close to the sup- 
porting base, and well removed from those 
sections of the electric circuit that are most 
susceptible to mechanical disturbances, aided 
in the production of a very stable fuze. On the 
other hand, it was found that the variations in 
turbine speed were somewhat greater than the 
variations in propeller speed of the other bomb 
fuzes. This appeared both as a greater spread 
in air travel to arming of individual fuzes un- 
der a given release condition and as a greater 
dependence of air travel on bomb size. 

Relative air travel on various bombs 
M-30 M-81 M-64 M-65 M-66 M-56 

1.00 1.02 1.24 1.48 2.32 1.87 

Two models, the T-82-E1 set for 3,600 ft 
MinSAT (not equipped with the arming delay 
bracket) and the T-82-E2 set for 2,000 ft 
MinSAT (equipped for arming delay device) 
were current at the end of World War II. The 
following data may be taken as representative 
of the principal characteristics of both models. 

The mechanical design of the T-82 is de- 
scribed in Chapter 4; its principal components 


Table 17. Pertinent features of T-82. 


Electrical 



Radio 



Circuit 

POD 


CF 

+ 16.7 


s( T f ^l v 100) 

12 


\/ p for R = °° / 



Audio 



PkAF 

184 


MvF (Pk) 

29 


MvF (140) 

37 


MvF (280) 

48 


C V (-volt) 

7.7 


EC (-volt) 

3.4 (20 to 35K) 

Proof performance* 



Burst height 

101 


Reflection coefficient 

0.8 


Proper (%) 

83 


Random (%) 

11 


Dud (%) 

6 


Physical characteristics 


Overall length (in.) 


8 

Length from shoulder (in.) 

3 

Overall width (in.) 


10 

Weight (lb) 


3% 

Manufacturer: 

Westinghouse 



* From 10,000 ft at 200 mph on M-81 or M-88. 


240 


CATALOGUE OF FUZE TYPES 



Figure 35. Power-oscillating-detector circuit 
used in T-82 bar-type White-carrier bomb fuze. 


are shown in Figure 28 of the same chapter. 
The arming mechanism has to be built more 
compactly than in the other bomb fuzes on 
account of the lower position of the generator ; 
otherwise it is essentially the same. 

The power oscillating detector used in the 
T-82 is shown in Figure 35. The component 
values given in Table 18 are for the T-82-E2, 
as required by Army Ordnance specification 14 
prepared in collaboration with Division 4. 


Table 18. Component values of POD oscillator in 
T-82 fuze. 


Resistor 

Value 

(ohms) 

Con- 

denser 

Value 
(w*f) Coils 

Turns 

R1 

100,000 

Cl 

500 1 

9 (antenna) 

R2 

6.8 

C2 

500 

6 (plates) 




(wound on same form) 

R3 

6.8 


2 

12 




3 

90 




5 

90 



Triodes 

: NR3A 



The nearly symmetrical oscillator assembly 
(on a phenolic block) is shown in Figure 28, 
Chapter 4. The two triodes are located on oppo- 
site sides of the central air duct, in line with 
the dipole bars. On a line at right angles are 
the interwound plate and antenna coils (top) 
and grid coil (bottom). The remaining oscilla- 
tor components are disposed in a symmetrical 
fashion with respect to these. 

The basic amplifier circuit of the T-82 bar- 
type bomb fuze is shown in Figure 32, Chapter 


3. The component values given in Table 19 are 
for the T-82-E2, as required by Army Ordnance 
specification, 14 prepared in collaboration with 
Division 4. 


Table 19. Component values for amplifier in 
T-82-E2 fuze. 


Resistor 

Value 

(megohms) Condenser 

Value 
(w*f ) 

R5 

2.2 

C3 

10,000 

R6 

0.3 

C4 

50 

R7 

115 ohms 

C5 

50 

R8 

3.3 

C6 

50 

R9 

3.3 

C7 

50 

R10 

4.7 

C8 

50 

Rll 

1.0 

C9 

0.1 ^ 

R12 

1.0 

CIO 

10,000 



Cll 

1,000 

R14 

330 ohms 

C13 

0.6 

R15 

1.0 

C14 

0.2 fii 

R16 

1.0 



R17 

30,000 ohms 



R18 

3,000 ohms 




Pentode : 

NS5 



Notes. For R20, see R2 and R3 in oscillator circuit for the T-82. 


A gain-control condenser C g shown in Figure 16, Chapter 3, is 
not present in the T-82 circuit, the gain of which may be adjusted 
by selection of suitable value for Cll. 

The transformer secondary is shunted by C3 and R6 in parallel 
instead of in series, as appears in Figure 16, Chapter 3. 

The general character of the amplifier assem- 
bly of the T-82 differs somewhat from that of 
the other bomb fuzes on account of space re- 
quirements of the central air duct. The assem- 
bly and its major parts are shown in Figure 13, 
Chapter 6. 

5 6 2 Navy Rocket Fuzes 

T-30 (Mk 171, Mod 0) Ring Type, 

Brown Carrier 

The fuze T-30, like the T-2004, was a bomb 
fuze modified for use on a Navy airborne 
rocket. The T-30 was intended primarily for 
attacking enemy aircraft with the HVAR. The 
weakness of enemy opposition in the air during 
the later stages of World War II made its pro- 
duction less urgent than that of some of the 
other fuzes. Although mass production (by 
General Electric) had barely started when 
World War II ended, considerable testing was 
done with the pilot production model (includ- 
ing a service test at the Naval Ordnance Test 
Station, Inyokern) and its properties were 
fairly well defined. 


SECRET 


PREPRODUCTION FUZES 


241 


Early functioning of the T-30 on account of 
the considerable afterburning of the HVAR 
propellant was a serious problem. The expedi- 
ent of delaying arming until afterburning was 
negligible and unsatisfactory because it gave 
an undesirably large minimum firing range. A 
program of research directed toward the elimi- 
nation of afterburning was partially successful, 
but the problem was by no means completely 
solved at the end of World War II. 

There was no fixed target testing with the 
HVAR. Consequently, the data presented in 
Table 20 for performance on this vehicle are 
limited to high-angle firing tests. 


Table 20. Pertinent features of T-30. 


Electrical* 


Radio 


Circuit 

OD 

CF 

+ 1 

S (volt) 

18 

Audio 


PkAF (c) 

69 

MvF (Pk) 

24 

CV (-volt) 

7.8 

EC (—volt) 

3.9 

Proof performance! 


ROA (ft) 

90 \ 

Proper + Mid (%) 

77 (Vehicle: HVAR 

Early (%) 

20 ( QE: 55° 

Dud (%) 

3 ) 

Physical and arming characteristics ( same as T-2004) 

Overall length (in.) 

10^2 

Length from shoulder (in.) 

4M 

Overall width (in.) 

3f 

Weight (lb) 

4 


* From General Electric units, 
t Bowen units; no data available on GE. 


The structure of the T-30 is practically the 
same as that of the T-2004 and the OD-circuit 
ring-type bomb fuzes and therefore requires 
no additional description. 

T-2005 

The T-2005 was the logical next step after 
the T-2004 and T-30 : a GP rocket fuze of small 
size making use of the designs being developed 
for mortar shell fuzes and provided with an 
external switch to permit selection in the field 
between two sets of characteristics appropriate 
to plane-to-plane or plane-to-surface firing. 
Test data are very scanty, and the characteris- 
tics of this fuze can be represented best by the 
tentative specifications that were completed 
immediately before the end of World War II. 


Some of the specification requirements are 
shown in Table 21. The fuze is shown in Figure 
46 of Chapter 4. 


Table 21. Pertinent features of T-2005. 



Plane- to-Plane 

Plane- to- 
Surface 

Vane 

Turbine 


Same 

Electrical 




Radio 




Circuit 

RGD 


Same 

CF 

-2 to -8 


Same 

S (volt) 

> 10 from 2K to 



20K ohms 


Same 

Audio 




PkAF 

60 to 100 


100 to 160 

MvF (Pk) 

15 to 30 


70 to 130 

MvF (75c) 



115 to 105 

CV (-volt) 

6.8 to 8.5 


Same 

EC (-volt) 

5.0 max 




(15K to 50K rpm) 

Same 

Physical characteristics 



Overall length 


4f in. 

Length from shoulder 

4f in. 

Overall width 


2 \ in. 

Weight 


28 oz 


The general design of the T-2005 (Figure 46, 
Chapter 4) is similar to that of the T-171. 
Since the ballistic effect of this fuze is less im- 
portant than that of the mortar shell fuzes, 
the antenna insulator is enlarged for increased 
strength. The safety and arming requirements 
placed on this fuze were rather complex, in- 
volving a number of users’ options. The mech- 
anism that was designed to meet these require- 
ments is not readily described; reference is 
made to Figure 47 and the accompanying text 
in Chapter 4. 

The electric circuit diagram of the T-2005 
is shown in Figure 36. 

3 6,3 Mortar Shell Fuzes 

T-132, Longitudinally Excited, White Frequency 

T-171, Longitudinally Excited, Brown Frequency 

T-172, Transversely Excited, Yellow Frequency 

All the mortar shell fuzes were considerably 
smaller than the rocket and bomb fuzes. In 
spite of this reduction in size, it was necessary 
to use the larger tail of the M-56 shell when 
they were mounted on the small M-43 mortar 
shell in order to obtain stable flight. They were 
designed primarily for use on 81-mm shells 
such as the M-43 and the M-56. 

The T-132 featured a radical innovation in 
electric construction: the production of a con- 


SECRET 


242 


CATALOGUE OF FUZE TYPES 


siderable part of the electric circuit by painting 
conducting material onto a ceramic base (see 
Chapter 6). This technique was designed to 
facilitate the maximum possible rate of pro- 
duction. 

Since immediate success of the new technique 
could not be assured, the T-171 was developed 
simultaneously, using standard components. 

Another innovation was the loop antenna, 
featured in the T-172. 

The three fuzes are shown in Figure 6, Chap- 
ter 1, and Figures 42, 43, and 44, Chapter 4. 
Except for the items mentioned above, they 
were quite similar in design. 

None had entered mass production at the 
close of World War II. Preparations for mass 
production of the T-132 had been completed. 
Considerable pilot production and develop- 
mental testing data are available for this fuze. 
Developmental testing data alone are available 
for the T-171 and T-172. Some use is made of 
specification requirements and design data in 
representing the laboratory characteristics of 
the latter two fuzes. 

The field performance scores for the mortar 
shell fuzes are of necessity averages over pe- 
riods involving a number of design changes. 
Although the scores are not impressive, they 
compare favorably with those obtained with 


Table 22. Pertinent features of T-132 (Globe-Union) 


Arming (yd) 

300 (approx) 

Vane 

Turbine 

Electrical 

Radio 

Circuit 

RGD 

CF 

+ 11.6 

S (volt) 

(11 at 6,000 ohms) 
( 9 at 20,000 ohms) 

Audio 

PkAF 

107 

MvF (Pk) 

44 

MvF (40) 

84 

CV (-volt) 

7.5 

EC (-volt) 

5.0 max* 

6.0 maxf 

Proof performance* 

Burst height (ft) 

8 

(over water) 

Proper (%) 

68 

Random (%) 

16 

Dud (%) 

17 

Physical characteristics 

Overall length 

41 in. 

Length from shoulder 

3f in. 

Overall width 

2 in. 

Weight 

22 oz 


* On raising generator speed from 20,000 to 80,000 rpm. 
t On lowering generator speed from 80,000 to 0 rpm. 
t On M-43 with M-56 tail charge: 1-4. QE: 45° to 80°. 



SECRET 



PREPRODUCTION FUZES 


243 


rocket and bomb fuzes at the same stage of 
development. Pertinent features are shown in 
Tables 22, 23, and 24. See Chapter 4 for further 
structural details of the mortar shell fuzes. 

The latest circuits of the mortar shell fuzes 
are shown, with component values entered 


Table 23. Pertinent features of T-171 (NBS). 


Arming (yd) 

300 (approx) 

Vane 

Turbine 

Electrical 


Radio 


Circuit 

RGD 

CF 

—5 to +5 

S (volt) 

4 min (60 and 90K) 

Audio 


PkAF 

80 to 120 

MvF (Pk) 

25 to 50 

MvF (40) 

60 to 140 

CV (-volt) 

6.6 to 8.7 

EC 

5.0 max* 


6.0 maxf 

Proof performance]: 


Burst height (ft) 

19 

(over water) 


Proper (%) 

67 

Random (%) 

13 

Dud (%) 

20 

Physical characteristics 

Overall length 

4f in. 

Length from shoulder 

3f in. 

Overall width 

2 in. 

Weight 

22 oz 

* On raising generator speed from 15,000 to 60,000 rpm. 

t On lowering generator speed from 

60,000 to 0 rpm. 

X On M-43 with M-56 tail charge: 2 

and 4. QE: 45°. 


thereon, in Figures 37, 38, and 39. The circuits 
for the T-132 and T-171 are taken from Army 
Ordnance specifications, 15 ’ 16 prepared in colla- 
boration with Globe-Union, Inc., National 
Bureau of Standards, and Division 4. The T-172 
circuit is taken from the final progress report 
of the Zenith Radio Corporation on this project. 

The ceramic oscillator block of the T-132 in 
various stages of “painting” of components and 


Table 24. Pertinent features of T-172 (Zenith). 


MinSAT (ft) 

800 

Vane 

Turbine 

Electrical 

Radio 

Circuit 

RGD 

CF 

+ 11 

S (volt) 

3 

Audio 

PkAF 

95 

Gain 

75 

Proof performance* 

Burst height (ft) 

23 

(over water) 

Proper (%) 

48 

Random (%) 

27 

Dud (%) 

25 

Physical characteristics 

Overall length 

6^ in. 

Length from shoulder 

5^ in. 

Overall width of body 

2 in. 

Diameter of loop 

3 in. 

Weight 

24 oz 


* On M-43 with M-56 tail charge: 2, 3, 4. QE: 45° to 80°. 



f SECRET 



244 


CATALOGUE OF FUZE TYPES 



the non-painted components and the complete 
assembly appear in Figures 10 and 7, Chapter 
6. In the latter figure, the triode is seen to be 
located in the center, in the position occupied by 
the generator shaft in earlier fuzes; the small 
white disks are the condensers. 

The latest model of the T-132 amplifier is 
shown in Figure 16, Chapter 6. The ceramic 


plate is mounted parallel to the longitudinal 
axis of the fuze. The figure shows both sides of 
the plate, in both the “painted” state and in 
the complete state. The reduction in size of this 
assembly, relative to that of the earlier fuzes, 
may be judged by comparing Figures 16 and 
17, Chapter 6, noting that the electron tubes are 
the same in both cases. 



Figure 39. 


Electric circuit of T-172 mortar shell fuze. 




SECRET 


INTRODUCTION 


Chapter 6 

PRODUCTION 


6.1 

I N the early days of radio proximity fuze 
development, many workers in the field were 
fearful that even though satisfactory models 
might be built in the laboratory by skilled peo- 
ple, the project would prove infeasible because 
those models could not be mass-produced suc- 
cessfully by unskilled labor in the huge quanti- 
ties needed by the Services. Those who later 
encountered and overcame some of the produc- 
tion headaches that arose were, if the truth 
were known, often of the same opinion. The 
successive problems that arose were resolved 
by the skill, perseverance, ingenuity, and op- 
timism of the technical and production staffs 
of the various manufacturers working in closest 
cooperation with physicists and engineers of 
the development staff. 

It is the purpose of this chapter to outline 
briefly some of the production procedures that 
were adopted, some of the problems that arose 
and their resolution, and, in general, to point 
out some of the considerations involved in the 
quantity production of generator-powered 
proximity fuzes. No attempt will be made to go 
into great detail regarding the manufacture of 
any one type of fuze. Each type naturally has 
its own peculiar production problems. 


6,1,1 Pilot Plant Production 

An effort was made to anticipate and over- 
come the difficulties likely to be encountered in 
mass production by means of pilot production 
of considerable quantities of each type of fuze 
in plants set up for that particular purpose. 
These plants produced varying quantities of 
preproduction models, in some cases as many 

a This chapter was prepared by A. S. Clarke of the 
Clarke Instrument Corporation, Silver Spring, Mary- 
land, and consultant to the Ordnance Development Di- 
vision of the National Bureau of Standards. Early in 
World War II, he was technical aide to Division 4, 
NDRC, and later manager of the Electronics Division, 
Bowen & Company, Bethesda, Maryland, engaged in 
pilot production of proximity fuzes. 


as 25,000 of a given type. The conditions under 
which these pilot plants operated were, to a 
considerable degree, the same as would be en- 
countered in large-scale production. The labor 
was unskilled, or at best semiskilled; produc- 
tion-line techniques were employed; and the 
fuzes were not babied or hand-fitted at any 
stage of manufacture. 

These pilot lines served several important 
functions in addition to developing production 
procedures and establishing an index of pro- 
duction feasibility and quality for the design. 
They served as a source of fuzes necessary for 
the extensive field testing of new designs, and 
they provided a flexible source of supply for 
fuzes modified from time to time as design 
changes were dictated by field test results, 
changes in tactical requirements, and by im- 
provements by the design group. 


6,1,2 Production Organization 

To a first approximation, an organization for 
mass production of proximity fuzes bears a 
very close resemblance to the setup usually em- 
ployed for mass production of radio receivers. 
They are similar in that both organizations (1) 
employ relatively unskilled labor, (2) break 
down production into a multiplicity of simple 
easily performed operations that can be quickly 
taught to such labor, (3) make use to the fullest 
possible extent of continuous production-line 
methods, and (4) employ similar tools and 
processes. The two organizations differ in that 
in the fuze plant (1) more frequent and more 
vigilant inspection is required, (2) closer liai- 
son is required between engineering and pro- 
duction departments, (3) more frequent test- 
ing with more elaborate equipment is required, 
(4) production supervisors should be of a 
higher caliber since the emphasis must be on 
quality of production rather than, primarily, on 
quantity, and (5) eternal vigilance regarding 
small and, in some other products, unimportant 
details must be the rule. 



245 


246 


PRODUCTION 


If there is any formula for the successful 
production of radio proximity fuzes, it would 
probably read like this: Mix together equal 
parts of careful workmanship, rigid inspection, 
intelligent and responsible supervision, and 
good production designs. 

A process flow chart showing the routing of 
fuzes through a typical plant is given in Fig- 
ure 1. 



Figure 1. Process chart for production of T-51 
fuzes, Zenith Radio Corporation (reference 17, 
Figure 3). 


Typical interior views of plants engaged in 
mass production of fuzes are given in Figures 
2 and 3. 

A typical plant layout is shown in Figure 4. 


6,1,3 Preproduction Planning and 
Preparation 

One consideration that is fully appreciated 
by every production man but often discounted 
by design and laboratory workers is the neces- 
sity for a truly tremendous amount of plan- 
ning and preparation for quantity production 


of even the simplest item. And the proximity 
fuze is no simple item. The whole process of 
mass production is a carefully integrated and 
very delicate mechanism with its various parts 
so interrelated and interdependent that a 
breakdown at any one point can throw the 



Figure 2. View of production line for T-50 fuze 
at Emerson Radio and Phonograph Corporation 
(Emerson photograph). 


whole plant into complete disorder. Before pro- 
duction justifying the name can begin, the 
following must be done: (1) all drawings must 
be completed, checked, and approved; (2) all 
tooling, including production jigs and fixtures, 



Figure 3. Another view of production line for 
T-50 fuze at Emerson Radio and Phonograph 
Corporation (Emerson photograph). 


must have been fabricated and checked ; (3) all 
test equipment must be completed, tested, and 
installed; (4) supervisors must be trained; 
(5) inspectors and test equipment operators 


i 


SECRET 


ft 


OSCILLATOR 


247 


must be trained; and (6) an adequate supply of 
every component or purchased subassembly 
must be on hand to support a continuous flow of 
production. 

Of course there were occasions when, because 
of the pressure of wartime urgencies, produc- 
tion was started in advance of complete prepa- 
ration as outlined above and some of the pro- 
duction difficulties that arose are directly trace- 
able to this situation. 


62 OSCILLATOR 

621 Introduction 

The design of the oscillator portion of vari- 
ous types of fuzes has been covered in consid- 


The Problem 

Basically, the problem is to mass-produce a 
high-frequency oscillator of relatively small 
size that will (1) feed adequate energy to a 
suitable radiating system, (2) have the requi- 
site frequency stability, (3) maintain the car- 
rier frequency constant or within specified 
limits from fuze to fuze, (4) give uniform out- 
put from fuze to fuze, (5) be mechanically 
rugged to withstand the shocks incident to 
service, and (6) generate in itself no spurious 
responses that might result in premature fuze 
detonation. 

All parts of the oscillator circuit of the fuze 
are in strong r-f fields. Any motion of these 
parts, either in relation to each other or to the 
chassis, will produce a signal on the grid of the 
amplifier tube that is indistinguishable from the 



Figure 4. Plant layout for assembly lines for the production of T-51 fuzes, Zenith Radio Corporation 
(reference 17, Figure 4). 


erable detail in previous sections of this report. 
No attempt will be made here to repeat this 
descriptive material, and it is presumed that 
the reader has studied and become familiar 
with it. The purpose of this chapter is to outline 
some of the procedures adopted in mass manu- 
facture to insure that the requirements for a 
satisfactory oscillator portion of the fuze are 
fully met. 


signal from the selected target that initiates 
normal functioning. For this reason, every 
effort must be made in production to produce a 
rigid r-f assembly. 

62 2 Typical Procedures 

Usually the production department is handed 
a layout and a model of the oscillator design. 


SECRET 


248 


PRODUCTION 


They are allowed little, if any, latitude in 
changing the layout of components or the 
method of oscillator construction. Even the 
“dress” of every lead is specified, since very 
slight variations in this respect might cause 
undesirable variations in carrier frequency 
from fuze to fuze. 

Incoming Inspection 

The first and a very important step in the 
production of satisfactory oscillator assemblies 
is adequate inspection of incoming components. 
Those resistors and condensers used in parts 
of the circuit having any effect on oscillator 
drive, carrier frequency, or coupling to the 
radiating system should be 100 per cent in- 
spected. To what extent tubes should be in- 
spected depends on the demonstrated reliability 
of the inspection at the source of supply. Me- 
chanical inspection should be made of the 
coil forms for such defects as improper cur- 
ing (poor mechanical strength), improperly 
cleaned flash, and uniformity of size. The oscil- 
lator mounting plate and tube shield assembly 
should be checked for flatness, plating finish, 
full complement of holes (small punches break 
easily), and quality of soldering of tube shields 
to the supporting plate. Molded oscillator blocks 
and all other chassis parts should be inspected 
for conformance to specifications. Mold pins 
making small lead holes in plastic parts are 
subject to frequent breakage and cases have 
been known where a considerable quantity of 
pieces have been molded and shipped before 
such breakage was noticed. 

Types of Oscillator Construction 

Three different types of oscillator construc- 
tion were in common use. Many of the mechani- 
cal features of the designs have already been 
discussed and illustrated in Chapters 3 and 4 
(cf. Figures 13, 14, and 15, Chapter 3) of this 
volume. For the purpose of discussion, the 
types of construction listed below will be cov- 
ered individually. 

Basic types of oscillator construction 

1. Phenolic block used for foundation. 

2. Thermoplastic block for foundation. 

3. Ceramic block used for foundation and in- 
corporating so-called printed circuits. 


Each type of construction presented its own 
peculiar production problems. All of the blocks 
had one common feature in that they made use 
of molded cavities to support components and 
employed cements of various kinds to anchor 
these components in place. 

Figures 5, 6, and 7 show oscillator assem- 
blies employing the three types of construction 
employed. 

Thermosetting Phenolic Blocks 

Where a mica-filled phenolic thermosetting 
material is used for the oscillator foundation, 
the first step is treatment to insure that all 
moisture is driven from the block and that the 
surfaces to which components are to be bonded 
are made ready to receive the bonding agent. 
Early production made use of a cement known 
as Amphenol 912, a product of the American 
Phenolic Corporation. This material does not 
adhere well to the glazed surfaces of the phe- 
nolic material as it comes from the mold. To 
overcome this, the blocks are sand-blasted, a 
treatment which also removes the glaze from 
the sides of the coil cavities. If these sand- 
blasted blocks remain very long in a humid 
atmosphere, there is a possibility of additional 
moisture absorption. To prevent this, after 
sand-blasting the blocks are placed in a well- 
ventilated oven or under infrared lamps and 
heated to a temperature of approximately 
150 F for a period of approximately three 
hours, after which they are given a coat of 
the 912 cement, which acts as a sealing agent 
against further moisture absorption and also 
furnishes a surface to which later applications 
of the same cement would adhere more firmly. 

It was found desirable by some producers to 
treat also the larger components, such as tubes 
and coil forms, with a light coat of the cement 
and allow same to dry thoroughly before as- 
sembly. This was found to aid materially the 
later cementing of these components in place. 

Later in the production program, cements 
were found that bonded thoroughly with ther- 
moplastic materials without the above sand- 
blasting treatment. 

Thermoplastic Oscillator Blocks 

When blocks of thermoplastic material were 


SECRET 


OSCILLATOR 


249 



Figure 5. Oscillator assembly using thermosetting plastic block. 



Figure 6. Oscillator assembly using thermoplastic block (Zenith photograph). 


250 


PRODUCTION 


used, sand-blasting and precoating components 
with cements was not necessary, since cements 
were available that fuzed with the plastic ma- 
terial to form a true bond. 

The use of thermoplastic material for the 
blocks had other decided advantages, one of 
which was the ability to tack down leads along 
the top surface of the block with a small hot- 


through the use of a thermosetting cement. 
Ceramic construction forms a special case 
which is covered in more detail later in this 
chapter. 

Oscillator Coil Construction 

In all fuze designs in use up to the end of 
hostilities, the degree of carrier frequency uni- 



Figure 7. Oscillator assembly using ceramic block (Globe-Union, Inc., photograph). 


pointed metal tool which softened the material 
sufficiently to allow the wires to be embedded 
firmly into the block at that point. 

Ceramic Blocks and “Printed” Circuits 

The use of ceramic oscillator blocks with so- 
called “printed” or “painted” circuits reduced 
very materially, but did not entirely eliminate, 
the number of loose components which had to 
be anchored to the block. The interconnecting 
wires and resistors were stenciled directly on 
the ceramic and fired so that they became inte- 
gral with the block. However, it was still neces- 
sary to mount securely such items as coils, 
tubes, r-f chokes, and condensers. This prob- 
lem was successfully overcome by the only 
manufacturer using this type of construction 


formity that could be obtained was solely de- 
pendent upon the uniformity of tube interelec- 
trode capacities, the production of uniform 
coils, and the reproducibility of wiring layout 
and stray capacities from unit to unit. There 
were no lumped capacities used in the fre- 
quency-determining circuits. All the above ex- 
cept uniformity of tube characteristics are 
under the control of the fuze manufacturer. All 
the factors influence not only the carrier fre- 
quency but also the amount of oscillator drive 
and coupling to the radiating element. 

The uniformity of carrier frequencies and 
oscillator output attained in production is 
illustrated by Figures 8 and 9, the data for 
which came from test on groups of approxi- 
mately 500 units of each of three different man- 


SECRET 




OSCILLATOR 


251 


ufacturers. As a matter of interest, the degree 
of carrier frequency uniformity achieved in 
production sometimes proved embarrassingly 
good, since, as a safety measure, some spread 
in carrier frequencies is desirable. 

The production of uniform coils is, in itself, 
no mean achievement. In fuzes using a thermo- 
setting mica-filled plastic for the oscillator 
block, it was customary to use the same ma- 
terial for the coil forms. These forms were 
usually transfer-molded in multiple molds with 


register between the two halves of the mold 
and the necessity for removal of flash. 

Coil leads were anchored in the above forms 
by drawing the wire through accurately drilled 
holes. These holes were drilled by inserting the 
form in a drill jig made from a small square 
block of steel having a close fitting hole for the 
form and provision for uniquely orienting the 
bosses on the end of the form with relation 
to the holes to be drilled. Transverse holes were 
then drilled through hardened drill bushings at 





Figure 8. Uniformity of carrier frequencies in 
production of radio proximity fuzes. 





Figure 9. Uniformity of oscillator grid voltage 
in large-scale production of radio proximity 
fuzes. 


removal from the mold accomplished by un- 
screwing the piece from the cavity which was 
essentially a tapped hole. A boss on the end of 
the coil form served as a key for the wrench 
used for removal. Another method used a two- 
piece mold with the flash line occurring along 
two flats on the side of the coil form. This latter 
method has the disadvantage of requiring exact 


the proper places. The mortality rate among 
the No. 70 drills used for this purpose was very 
high, due to the highly abrasive character of 
the phenolic material. 

All coils were wound by hand, using simple 
winding fixtures in which the coil form was 
turned by a crank which engaged the bosses on 
the ends of the form. Before winding, the forms 



252 


PRODUCTION 


were given a coat of Amphenol 912 cement and 
dried. After winding, another coat of cement 
was applied and allowed to dry thoroughly be- 
fore the coil was inserted in its cavity and 
cemented in place. 

Coil forms molded of thermoplastic material 
were a decided improvement in that it was pos- 
sible to anchor the start and ending of the 
winding by tacking the wire to the form 
through the use of a small heated metal point. 
In this manner it was possible to avoid some of 
the troubles encountered in making uniform 
coils in which the leads had to pass back 
through the transverse holes drilled in the 
form. In some cases, the wire emerged from the 
form on the bottom or blind side of the coil and 
had to be dressed back to the top of the chassis 
block along the outside of the form, giving a 
long and often indeterminately positioned lead 
which sometimes resulted in variations in car- 
rier frequency and loading and coupling. With 
the thermoplastic forms, the actual end of the 
helix of the coil could be located as desired on 
the circumference of the coil, and while dou- 
bling back of leads was sometimes necessary, 
at least there was no wire threaded through an 
oversized hole with the attendant worries as to 
whether or not the lead could flop around in 
the field of the coil. 

On fuzes using interleaved and center-tapped 
windings feeding transverse dipole antennas, 
the center lead was usually formed by twisting 
together an uncut loop in the continuous wind- 
ing by means of an auxiliary fixture mounted at 
right angles to the coil axis and having a crank- 
actuated retractable button hook arrangement 
around which was looped this center lead. 
Turning the crank twists together the loop. 
This twisted Formvar pair of coated wire then 
had the insulation removed by dipping it in 
what was essentially a superheated solder pot. 
This pot was a metal tube approximately 4 in. 
long and % in. in diameter surrounded by an 
electric heating element which kept the melted 
solder at a temperature of approximately 
1200 F. Since the pot diameter was small, only 
a very little area of the solder pool was exposed 
to oxidation. At the temperature used, the 
Formvar insulation immediately melted off and 
wires became well tinned and intimately con- 


nected as a single lead. This lead could then be 
cut to the proper length without unraveling. 

The production of coils wound on ceramic 
forms is covered in a special Section 6.2.3. 

Mounting of Tubes in Oscillator Assembly 

One of the oscillator components most diffi- 
cult to mount securely in the assembly is the 
tube, or tubes if a diode is also used. Many ex- 
pedients were devised for this purpose; some 
of the more successful ones are described. As 
can be seen in Figures 5, 6, and 7 (also Figure 
8, Chapter 3), the tubes used for oscillators 
were, in the majority of cases, oval in shape, 
having two relatively broad flat sides with nar- 
row rounded ends. The glass seal-off tip on the 
end of the tube was the only portion that 
approached the rounded bottom of the tube 
well, and at best the tube was in contact with 
the round metal shield at only three points. 
The problem then is how to overcome this 
basically weak mechanical design. 

By far the majority of early fuze production 
had the tubes cemented in place. Toward the 
end of the program, other and better methods 
had come into use. In cementing in tubes, using 
the aforementioned Amphenol cement, there 
was always the possibility of getting too much 
cement in the tube shield and having it “case- 
harden.” This name is given to a particularly 
undesirable condition that arises when a hard 
film forms on the surface of the pool of cement 
during rapid initial evaporation of the solvent. 
This hard film then serves as a trap which 
prevents the further evaporation of the re- 
maining solvent, which in the course of time 
permeates and softens that portion of the 
previously dried cement that was presumably 
holding the tube in place. The same condition 
also prevailed in cementing coils in the cavities 
provided for them in the oscillator block. 

One method of preventing the above difficulty 
and of insuring a fairly uniform application of 
cement all over the block was evolved and 
promptly dubbed the “fruit jar” technique. 
Here the cement of carefully controlled vis- 
cosity was contained in a round-mouthed jar 
and the oscillator assembly placed top down 
across the mouth of the jar. The whole was 
then inverted so that copious quantities of the 


OSCILLATOR 


253 


cement permeated every cavity on the block and 
completely surrounded all components, includ- 
ing the tube. The jar was then returned to the 
normal position and the surplus cement allowed 
to drain back into the jar. Sufficient cement was 
retained around the components in the cavities 
and tube wells through capillary attraction to 
form well-defined fillets which, since they con- 
tained a minimum volume of cement, dried 
hard quickly and adequately held the compo- 
nents. 

When the above cement dunking process 
was combined with shaped tube shields, the 
ultimate obtainable with the cementing method 
of tube placement resulted. Shields were shaped 
by inserting a mandrel having approximately 
the same size and shape of the tube into the 
normally round tube shield and squeezing the 
shield around it. The result is a shaped well 
which is a neat push fit for the tube with 
several points of contact between the tube 
and the shield. Even where there is no con- 
tact, the separation is so small that cement was 
retained in the space after the dunking process. 

One manufacturer used glass wool wrapped 
around the tube before insertion in the shield. 
This wool served to cushion the tube slightly 
and its compressibility permitted a neat wedge 
fit of the tube in the shield. Somewhat the same 
effect was obtained by another manufacturer 
who used a rubber cushion around the tube. 

Toward the end of the production program, 
a tube potting compound was evolved consist- 
ing of 80 per cent microcrystalline wax and 20 
per cent polyisobutylene. This molten mixture 
sets up rapidly upon cooling, providing a secure 
anchor for the tube. The technique is fast and 
simple and lends itself admirably to rapid pro- 
duction. It was in use by at least two manufac- 
turers. 


6 ' 2 ' 3 Production of Ceramic 

Oscillator Assemblies 

As mentioned previously in this report, the 
T-132 fuze employed unique methods of con- 
struction based on the use of so-called “printed” 
circuits on steatite plates and blocks. Because 
of its advantages and potentialities for future 


$ 


use, it seems advisable to present as much in- 
formation as is available on this type of fuze 
construction in this special section of this chap- 
ter. All the information is from a report by the 
Globe-Union Company to Division 4, NDRC, on 
development work performed under an OSRD 
contract on development work on this type of 
construction. 8 

This design is built around the process of 
forming the interconnecting leads and resistors 
for the circuit by the application of conducting 
and semiconducting materials directly to the 
surface of molded ceramic plates or blocks and 
the subsequent baking or firing of such ma- 
terials to the extent that they form virtually 
an integral part of the block itself. The tech- 
niques used for metalizing and resistoring are 
considered by Globe-Union to be trade secrets, 
although they state in the same report that the 
general methods are well known to the art. It 
is important to realize that the end result may 
be obtained by different manufacturing proc- 
esses, and it is not essential that the identical 
processes and techniques employed by Globe- 
Union be used. The metalizing art is an old 
development of ceramic and glass industries 
and there are many widely used methods of 
metalizing in use by the industry. The resistor- 
ing process incorporates the processes devel- 
oped in the making of variable resistors and 
this too is a widely known art. 

Construction of Ceramic Oscillator Block 

The oscillator block is shown in Figure 7. The 
steatite used has passed the Army and Navy 
qualifications tests in accordance with JAN 
Specification 1-10 and is known as a grade L-5 
ceramic. The properties of the material are 
tabulated below. 


Mechanical 


Specific gravity 
Modulus of rupture 
Tensile strength 
Compressive strength 
Coefficient of thermal 
sion 

Moisture absorption 
Impact strength 

Power factor 
Dielectric constant 
Loss factor 
Dielectric strength 


2.5 

20,500 psi 
9,100 psi 

76.000 psi 

expan- 

6.9 X 10-6 20 to 100 C 
Less than 0.02 per cent 

2.0 ft-lb per in. 
Electrical 

0.110 per cent (1 me) 
5.82 (1 me) 

0.640 per cent (1 me) 
247 v per mil 


Secret 


254 


PRODUCTION 


Because of the large and intricate shape of 
the block, it was molded by the wet process to 
provide better flow characteristics in the mold. 
Allowance for shrinkage during firing was 
made. Figure 10 shows the block as it comes 
from the mold. At this stage, it is completely 
formed except for the outside dimensions and 
the two large coil holes. The coil holes were 


the ceramic, a thin film of silver was applied to 
the ceramic as described below. Additional 
coats of copper, tin, and solder were applied to 
the base coat of silver on certain parts of the 
block where it was desired to reduce the electric 
resistance of the coating to a very low value or 
to facilitate soldering to heavy metal parts, 
such as the support member and the shell. 



Figure 10. Ceramic oscillator block in advanced stages of preparation. View in upper left shows block 
as it comes from mold. (Globe-Union, Inc., photograph.) 


drilled and the outside grooves and proper di- 
mensions were obtained by machining opera- 
tions. The block is then fired in a kiln to pro- 
duce a hard, white, vitrified material. 

Construction of Ceramic Coil Forms 

The oscillator, antenna, and choke coil forms 
were extruded in the form of rod from the same 
type of material used for the oscillator block. 
All three forms were fluted to facilitate wind- 
ing and both antenna and oscillator coil forms 
are threaded for accurate spacing of the wind- 
ing. Threads and lead holes were machine cut 
in separate operations before the forms were 
fired. 

Metalizing of Oscillator Block 

To provide circuit connections and means of 
fastening other metal parts to the surface of 


The material used for silvering consisted of 
finely divided silver powder in a suitable ve- 
hicle. Before application, the surface of the 
ceramic was thoroughly cleaned to remove all 
trace of oil and dirt. After it was applied, the 
piece was fired in an oven to burn out the 
vehicle and cause the individual particles to 
coalesce, forming a continuous film which ad- 
heres tenaciously to the surface of the ceramic. 

Owing to the irregular shape of the oscillator 
block, the silvering material was applied by a 
roll to the edge and by brush to the circuit ele- 
ments. The edges were silvered to enable the 
shell and support member to be soldered di- 
rectly to the block. A tracing template was used 
to position accurately the location of the sur- 
face connections and a small brush was used to 
apply the material to the surface. 

Both edges were given a plating of copper 



OSCILLATOR 


255 


and tin over the initial silver coat to facilitate 
soldering. All high-current leads were copper- 
plated to provide low-resistance paths. The 
average thickness of the silver coating was 
approximately 0.0002 in. 

Resistoring Process 

The process of resistoring on the ceramic 
surface consisted of applying a suitable resist- 
ance material between two metalized elements 
on the surface. The resistor material consisted 
of a base of conducting particles, such as car- 
bon black or graphite, in a suitable vehicle. The 
surface to be coated was covered with a mask 
having suitable cutouts to outline the areas on 
which the material was to be deposited and the 
material was applied to the surface by spray- 
ing. After spraying, the resistor was air dried, 
the mask removed, and the resistor baked to 
stabilize the resistance. After baking, the re- 
sistor was checked for value, and if any adjust- 
ment was needed it was made by scraping 
away a little of the resistance material to in- 
crease the resistance value. This was possible, 
since in the spraying operation the low side 
of the resistance tolerance was favored. Once 
the resistor was adjusted, it was given a pro- 
tective coating of varnish. 

A number of factors are important in deter- 
mining the resistance value. The variable fac- 
tors are the ratio of the conducting particles to 
the vehicle or binder, and the length, width, 
and thickness of the deposit. The air pressure 
used in the spray gun and the baking time were 
found to have no appreciable effect on the re- 
sistance value. 

Resistors made as above described exhibit a 
slight negative voltage characteristic, as shown 
in Figure 11, and have good stability under 
adverse humidity conditions. Tests have indi- 
cated that they will dissipate approximately 
0.3 to 0.4 watt for a period of 250 hours with a 
decrease in resistance of only 7 per cent. 

Soldering to the Ceramic Surfaces 

Special techniques for soldering to the ce- 
ramic were used in order that the following 
requirements could be met: (1) that the solder- 
ing process not weaken the ceramic because of 
heat shock, (2) that initial strains not be de- 


veloped in the ceramic because of excessive 
shrinkage of the solder upon cooling, and (3) 
that the solder not dissolve the thin film of 
metal on the surface of the ceramic. The use of 
special low-temperature low-contraction solder 
such as RM 275, together with preheating of 
the ceramic, prevents heat shock from occur- 
ring. For soldering directly to the silver coat- 
ing, a special low-temperature silver alloy 
solder such as RM 297 was used. Use of silver 



Figure 11. Variation of resistance with voltage 
for “painted” resistors used in ceramic assem- 
blies. 


alloy solder prevents the silver deposit on the 
surface from being dissolved into the solder, 
since the solder is already saturated with silver. 

Ceramic disk capacitors and wire leads were 
soldered directly to the ceramic using the ap- 
propriate solder. The resulting bond between 
metal and ceramic was very strong, and it is 
possible to rupture the ceramic before the joint 
will fail. 

Ceramic disk condensers are soldered directly 
to appropriately located silvered points on the 
plates. This was very simply done by heating 
the disk capacitor to a temperature sufficient 
to melt the solder, applying a small amount to 
one face and pressing it against the ceramic 
plate with sufficient heat to cause the solder to 
bond to the silvered surface of the plate. Con- 
nection to the top side of the condenser is made 
by soldering a small strip of metal ribbon to 


SECRET 


256 


PRODUCTION 


that surface, the ribbon then being connected 
to any desired point of the circuit. 

The soldered joints between the oscillator 
block and the shell and support member are 
very critical, since the even distribution of the 
weight of the unit to the oscillator block is de- 
pendent upon the quality of these joints. The 
block was grooved at these two joints to pro- 
vide a capillary trough to insure that there was 
a secure bond between the inner face of the 
shell and support member to the block. In 
soldering these joints, the operator was re- 
quired to use a precut specified amount of 
solder to insure that the joints were completely 
filled. 

Assembly of the Ceramic Oscillator Block 

Assembly of the tubes, coils, and chokes to 
the oscillator block presented a mechanical 
problem due to the axial mounting of these 
parts and the necessity of their remaining in 
fixed position during setback. Coils, chokes, 
and tubes were first held in place with polysty- 
rene cement. This cement was chosen because 
of its excellent high-frequency dielectric prop- 
erties, but its use necessitated long and careful 
drying under infrared lamps. The tube was 
held in place in the oscillator block tube well 
by wrapping the base of the tube with glass 
wool and impregnating the wool with polysty- 
rene cement. This made a large mass wetted 
with the cement and which dried very slowly 
even under the application of considerable heat. 
A film would form over the surface, preventing 
the rapid evaporation of the remaining solvent. 
In many cases, tubes thus cemented slid out of 
position during setback, and it was found nec- 
essary to devise another method of holding the 
tube. This was accomplished by cementing the 
tube in place with a thermosetting cement. The 
tube was positioned by a jig and the tube well 
filled with cement up to the level of the leads. 
In order that the cementing time required for 
the blocks be reduced to the minimum and the 
long drying cycle previously necessary for the 
polystyrene cement be eliminated, the coils and 
chokes were also cemented in place with the 
thermosetting cement. A subsequent baking 
cycle of 3 hours hardened the cement. 

All oscillator block assemblies were ad- 


justed to draw a total plate current of a speci- 
fied value by the addition of a padder resistor 
of conventional construction mounted axially 
in the block. After cementing, the necessary 
value of resistance was determined and the 
proper resistor attached to the block. Polysty- 
rene cement was used to anchor this resistor 
in place; however, due to the heavy leads by 
which it was attached, the resistor was self- 
supporting and thorough drying of the cement 
before further assembly work was not found 
necessary. 

The assembled oscillator block, together with 
all the components entering into the assembly, 
.is shown in Figure 7. 


AMPLIFIERS 

6,3-1 Requirements 

The essential characteristics of amplifier de- 
signs for satisfactory fuze operation have been 
covered in Section 3.2 of this volume. This pre- 
vious discussion does not deal with methods of 
construction nor with the various processes 
and procedures used in mass production of am- 
plifiers having the desired electric character- 
istics. 

The production department is usually handed 
a circuit diagram, a model of the type of con- 
struction proposed by the engineering depart- 
ment, a set of specifications covering perform- 
ance of the finished unit, and a list of the pre- 
cautions and procedures found necessary by 
the engineering department in their model 
work on that particular design. From this point 
on, it is the responsibility of the production 
department to mass-produce amplifiers having 
the desired characteristics and meeting the 
stated specifications with the least possible 
assistance from the engineering and develop- 
ment group. 

The two basic requirements of the amplifier 
are that it have the desired gain and shaping. 
At this point it should be pointed out that the 
term “gain” as used in connection with fuze 
production does not have quite the same conno- 
tation as it ordinarily possesses. The gain of 
the amplifier system, as such, is seldom meas- 


SECRET 


AMPLIFIERS 


257 


ured in production. What is actually measured 
is the overall figure of merit known as “milli- 
volts to fire.” This takes into account the effec- 
tive critical voltage of the thyratron and the 
amplitude of hum (generator ripple) and 
spurious voltages originating in the amplifier 
circuit. 

The necessity for shaping the amplifier gain 
characteristic for the desired frequency re- 
sponse has been thoroughly covered in Section 
3.2. Examples of the shaping necessary to meet 
the basic requirements have been shown and 
methods of obtaining such shaping discussed. 


the amplifier which critically affect the gain 
and shaping should be 100 per cent inspected. 

Obviously, the type of circuit employed in- 
fluences the mechanical layout and construction 
of the amplifier. The four principal types of 
construction employed in fuzes that reached 
the production stage were as follows: (1) 
sandwich or wafer, (2) ring or collar, (3) 
printed circuits on ceramic plates, and (4) disk. 

Sandwich Construction 

A typical amplifier using the sandwich type 
of construction is shown in Figure 12. In this 



Figure 12. Sandwich-type assembly for amplifier. 


Procedures 

It is the purpose of this section of the chap- 
ter to deal with types of amplifier construction 
and the various manufacturing procedures em- 
ployed. 

As with the oscillator, the construction of 
satisfactory amplifiers begins with inspection 
of incoming components. Those components of 


construction, two punched linen Bakelite plates 
approximately % 2 in. in thickness are held 
apart in a suitable jig and most of the resistors 
threaded through holes in the plates. The two 
plates are then pushed together with the re- 
sistors acting as spacers. This foundation then 
passes down the production line and has pro- 
gressively added to it other resistors, con- 
densers, and tubes. 


SECRET 


258 


PRODUCTION 


This type of construction has certain advan- 
tages and, as usual, certain disadvantages. The 
construction results in a rigid assembly and 
shorter leads than is possible with any other 
method using conventional components. It has 
one decided disadvantage in that it is not pos- 
sible to replace a defective resistor after the 


One variation of the sandwich-type construc- 
tion is shown in Figure 13. This design was 
evolved because of the need for an unobstructed 
passage for air to operate an internal turbine 
(T-82 fuze). Two round Bakelite disks having 
a central hole for the air tube are utilized. On 
the two disks are mounted the electric com- 



Figure 13. Sandwich-type assembly for amplifier with central opening. 


sandwich is put together. In practice, however, 
this has not proved as much a drawback as it 
might seem, since very few amplifiers get 
through with defective or incorrect resistors in 
place. 


ponents with some of the larger components 
sandwiched in between. This type of construc- 
tion was used by one manufacturer only (West- 
inghouse), and large-scale production was just 
beginning at the end of hostilities. 


AMPLIFIERS 


259 


Ring Construction 

The ring or “dog collar” type of construction 
found considerable favor with production peo- 
ple. The majority of the fuzes manufactured 
(particularly T-51) used this type, a typical 
example of which is shown in Figure 14. In this 
construction, a strip of Bakelite or fish paper 
is punched to receive either eyelets or, in some 
cases, lugs for attachment and interconnection 
of various resistors and condensers which are 
attached to one end and, in the case of some 
manufacturers, both sides of the strip as it 
progresses down the production line. At some 
point in the line, the strip is bent into a circle 


Several different types of amplifiers were de- 
signed making use of this process. One, shown 
in Figure 15, was essentially a sandwich 
composed of two horizontally mounted ceramic 
plates containing “printed” resistors and inter- 
connections, between which were mounted the 
larger paper condensers and tubes. This type 
of construction was abandoned because of me- 
chanical weakness and replaced by a single 
ceramic plate mounted on edge for greater 
resistance to breakage under setback condi- 
tions. This amplifier is shown in Figure 16. 
This illustration shows the ceramic plate am- 
plifier in various stages of production. At the 



Figure 14. Ring-type assembly for amplifier (Zenith photograph) . 


and the two ends riveted together. This ring, 
or collar, is then inserted in the amplifier 
cavity. Because of its shape, this design prob- 
ably makes for maximum utilization of the 
space available. All components are accessible, 
and amplifiers having defective components or 
incorrect values installed can be readily sal- 
vaged. 

Ceramic Amplifiers 

The “printed” circuit on ceramic plates car- 
ries out the same methods of construction as 
were discussed in some detail in Section 6.2.1. 


right is the plate after all silvered interconnec- 
tion jumpers have been fired on. Second from 
the right shows the plate with all resistors in 
place, while the two views to the left show 
opposite sides of the finished amplifier with all 
paper and ceramic condensers and tubes in 
place. The methods of applying resistors and 
interconnection leads on these plates was iden- 
tical to those described in the portion of this 
chapter covering oscillators (see Section 6.2.3). 

Disk Construction 

This disk construction, which is illustrated in 


SECRET 


260 


PRODUCTION 



Figure 15. Components and assembly of ceramic-type amplifier, early version (Globe-Union, Inc., 
photograph). 



Figure 16 . Components and assembly of ceramic-type amplifier, late version (Globe-Union, Inc., 
photograph) . 







AMPLIFIERS 


261 


Figure 17, is, in reality, a variation of the 
sandwich previously discussed. The view shows 
two types of disk construction as compared 
with a conventional sandwich assembly shown 
in the center. The components are laid flat 
against the upper and lower surfaces of two 
suitably punched Bakelite strips and wired up, 
the two plates later being interconnected to 
form the amplifier assembly. The construction 
provides for maximum accessibility during 
fabrication and was particularly favored by 
one manufacturer. 

Gain-Control Condensers 

The methods of construction used in gain- 
control condensers is of considerable interest. 
These small capacitors, which are used to ad- 


change is made by peeling off more or less of 
the wrapped wire. This provides a method for 
changing the capacity in very small increments. 
One of the finished condensers of this type is 
shown just below the tubes in Figure 12. In 
fuzes using the ceramic plate construction, it 
was the practice to determine the amount of 
capacity needed by means of a continuously 
variable condenser, which is part of the ampli- 
fier test fixture, and then to select from previ- 
ously graded groups of condensers the indi- 
cated size of fixed capacity, which was then 
wired permanently into the circuit. This 
method consumed about the same amount of 
time as the adjustment of a gimmick wire and 
has the important advantage that it makes for 
greater stability in the amplifier and less 



Figure 17. Disk-type of amplifier assembly showing comparison with sandwich type. Latter is in center. 


just the gain of the amplifier by control of re- 
generation, vary in capacitance from approxi- 
mately 2 to 30 \i\if. The majority of manufac- 
turers used a modification of what is termed a 
gimmick in radio receiver manufacturing par- 
lance. In this device, the capacity is formed be- 
tween a piece of enameled copper wire, usually 
about size 18, acting as a mandrel, and a piece 
of smaller diameter enameled wire wrapped 
tightly around it. The enamel insulation on the 
two wires forms the dielectric, and capacity 


change of amplifier characteristics with pot- 
ting. Attention is called to the precautions nec- 
essary to protect the gimmick type of condenser 
from changes in capacity due to the potting 
materials and process which are described in 
the next section. 

Potting and Impregnating Procedures 

It was required that all amplifier assemblies 
be embedded in a potting compound in order 
that the electric characteristics would remain 


EGRET 


262 


PRODUCTION 


stable throughout the various conditions of 
storage and use. Usually, some preliminary im- 
pregnating processes were necessary before 
final potting (see Section 4.7.6). 

In amplifiers using Bakelite or fish-paper 
strips as the foundation, precautions are nec- 
essary to prevent these materials from absorb- 
ing atmospheric moisture, which might result 
in relatively low-impedance paths across criti- 


40, 



z 40. , 



Figure 18. Uniformity of frequency of peak 
audio amplification in large-scale production of 
radio proximity fuzes. 


cal portions of the circuit and adversely affect 
the operation of the amplifier. 

One manufacturer’s procedure involved the 
immersion of the fully punched amplifier ter- 
minal strip and also the insulator strip, used 
to prevent shorting of components to the metal 
case, in hot ceresin wax until all bubbling 
stopped. All the amplifier parts and tubes are 
then mounted and the entire assembly again 
impregnated with hot ceresin. After cooling, 
it is then flash-dipped so that a heavy protec- 
tive layer of wax is deposited on all parts. 
These treatments serve to drive out and keep 


out moisture and at the same time prevent any 
appreciable, if not all, deleterious effects from 
the tung oil potting compound. 

Essentially the same procedure was followed 
by other manufacturers, about the only varia- 
tion being that instead of ceresin, some manu- 
facturers used commercial microcrystalline 
waxes sold under such trade names as Superla 
or Halowax. 

One interesting variation of the above pro- 
cedure was used in pilot production of T-30 
fuzes. This procedure might prove awkward in 
large-scale operations because of the larger 
quantities of assemblies involved. In order to 
drive out all moisture before impregnation, the 
day’s production of completed amplifier assem- 
blies (before installation of the gain-control 
condenser) were accumulated and placed on top 
of cold hard Superla wax contained in pans. 
These were then placed in an oven, together 
with an active drying agent, and baked at about 
70 C for 8 hours. During the first 4 hours, the 
wax does not become sufficiently molten to 
allow the amplifier assemblies to sink below the 
surface. Thus, the amplifiers were actually 
baked in a drying atmosphere before impreg- 
nation. After the wax completely melts, the 
amplifiers sink and are cooked for the next 4 
hours in the hot wax. Probably the only way to 
improve on this process is to vacuum impreg- 
nate the amplifiers, but this procedure is some- 
what awkward where wax is used as the im- 
pregnating agent. 

The gimmick-type gain-control condensers 
must be protected against the action of the tung 
oil potting material. Many schemes were tried, 
the most successful being the boiling of the 
finished condenser assemblies, with the ends of 
the wound wire twisted together, in Zophar 
Mills No. 1563 Wax at about 150 C for 4 hours 
to drive out air and fill all cavities with the 
wax. The condensers are then removed, the 
free ends of the outside wire clipped short, and 
the condensers boiled for another 4 hours in 
order to allow the winding to assume a relaxed 
or normalized condition. This tends to avoid the 
effect of further unwinding and the resulting 
change of capacity after adjustment of the gain 
of the amplifier. 

After the above treatment, the gain-control 


SECRET 


AMPLIFIERS 


263 


condensers were inserted in amplifiers previ- 
ously impregnated as described and gain ad- 
justment and final check made on the amplifier. 
The accepted amplifiers were then flash-dipped 
again in Super la wax at about 75 C to seal off 
the clipped end of the gimmick wire against 
moisture absorption. 

It is interesting to note the degree of uni- 
formity obtained by various manufacturers in 


facturer at the Central Testing Laboratory at 
the National Bureau of Standards. 

Before potting amplifiers in the fuze cavities, 
it is desirable to preheat the fuze by baking in 
an oven for about 1 hour at 45 C. This baking 
process accomplishes two results: (1) it dries 
out the amplifier cavity, and (2) it provides 
a warm surface for contact with the tung oil. 
This hastens the polymerization and minimizes 




Z 111 

3 I 




Figure 19. Uniformity of millivolts to fire in mass production of three different types of radio proximity 
fuzes: A, maximum and minimum values of millivolts to fire shown throughout broad pass band of T-51 
amplifier: B, spread in peak millivolts to fire is shown for narrow pass-band amplifier of T-90 (top) and 
T-89 (bottom). 


holding the peak audio frequency and milli- 
volts to fire at peak audio frequency to the de- 
sired limits. The spread of the peak audio-fre- 
quency values around the design center for 
three different manufacturers are shown in 
Figure 18. Figure 19 shows the spread of milli- 
volts to fire at peak frequency around the de- 
sign center for three different manufacturers. 
These figures are based on an analysis of tests 
made on approximately 500 units of each manu- 


the time during which the active tung oil mix 
can attack the wax on the amplifier assembly. 
Wax is a better insulator than tung oil, so that 
for the purposes of amplifier uniformity, re- 
moval of the wax coating must be prevented. 
If quick polymerization is effected, less harm 
is done to the wax. 

The proportions of tung oil and polymerizer 
used by different manufacturers varied from 5 
parts of tung oil to 1 part polymerizer to as 


ECRET 


264 


PRODUCTION 


high as 15 to 1. Since the polymerizer is slightly 
corrosive, there is some advantage in using as 
little of it as possible. The high ratio of tung oil 
to “hardener,” however, does make the setting- 
up time of the material longer. 

The polymerizer, or hardener as it was usu- 
ally called, was available from Westinghouse 
as an already prepared material, and most 
quantity manufacturers used this source of 
supply. Instructions for the preparation of this 
hardener are included here as a matter of rec- 
ord. The quantities given are for 1 gallon of 



Figure 20. Vacuum fixture for potting ampli- 
fier units (Globe-Union, Inc., photograph). 

hardener: ferric chloride, 6.4 oz by weight; 
tri-cresyl phosphate, 1 lb 2 oz by weight, castor 
oil, 3 pt, 7 fluid oz. 

Great care must be given to the handling of 
the hardener ingredients, particularly the an- 
hydrous ferric chloride, in order to guard 
against contamination with moist air. The an- 
hydrous ferric chloride is added slowly to the 
tri-cresyl phosphate, stirring constantly with 
a motor-driven stirrer for 2 hours. This should 
be done in a narrow-mouthed container to re- 
duce the circulation of air over the exposed 
surface and the amount of surface exposed. The 
castor oil is then added and stirred until thor- 
oughly mixed. The hardener is then poured 
into sealed containers. 

The hardener and tung oil are combined and 
thoroughly mixed by a motor-driven stirrer in 
a covered container for approximately 5 min- 
utes, after which it is poured into the amplifier 
cavities. Owing to the viscosity of the mix, sev- 
eral intermediate pourings are usually required 


as the level gradually settles. After pouring, the 
fuzes are then returned to an oven held at 
approximately 45 C and kept there for approxi- 
mately an hour to hasten polymerization. 

Different methods of setting up the potting 
operation as an integral part of the production 
line were devised by different manufacturers. 
In one plant, the conveyor belt was routed by 
an air-conditioned room in which all mixing 
and pouring operations were conducted. The 
units were placed on the conveyor belt and car- 
ried through the preheating oven. As they 
passed a window of the mixing and pouring 
room, the rack containing a group of units was 
pulled through the small opening into the pot- 
ting room where the units were filled. The rack 
was then placed back on the belt and the units 
continued on through the oven for a sufficient 
length of time to permit setting up of the ma- 
terial. 

In another plant, the materials were mixed 
in large refrigerated containers and dispensed 
from this central point to a number of small 
containers on the assembly line, also refriger- 
ated, and the units filled by gravity flow from 
these secondary containers. 

Large refrigerated tanks were used on the 
line of another manufacturer, each holding 
approximately 15 gallons of the potting mix- 
ture. These tanks were equipped with motor- 
driven agitators to keep the mixture continu- 
ally stirred to prevent separation or stratifica- 
tion of the hardener and tung oil. Air was 
applied under pressure to the top of these tanks 
and the mixture was consequently ejected rap- 
idly into the fuze cavity through flexible plastic 
tubes. 

One manufacturer used a vacuum potting 
process which is of some interest. The fixture 
used is shown in Figure 20. The glass tubes 
were filled with the tung oil mix to the height 
marked on the tubes. The units were placed in 
a vacuum tank made of heavy plate glass. After 
the desired degree of vacuum had been drawn, 
the stopcocks were opened and the liquid flowed 
rapidly into the fuze directly underneath the 
tube. It was claimed by the manufacturer that 
this method of potting resulted in better pene- 
tration of the potting compound into the voids 
in the fuze cavity. 



NOSE ASSEMBLY 


265 


In addition to the tung oil mixture described 
above, two manufacturers used what was 
known as “Glidden” potting compound made by 
the Glidden Company, of Cleveland, Ohio. This 
material is a mixture of linseed oil, fatty acids, 
rosin, magnesium oxide, and alkaline-washed 
linseed oil. Its use requires the same careful 
temperature control as tung oil to prevent pre- 
mature setting up. It is slightly more difficult to 
pour and is not quite as good mechanically as 
tung oil, but it has a very decided advantage 
over tung oil in that it is not as corrosive. One 



Figure 21. Arbor press for staking windmill 
bearing assemblies. 


manufacturer using Glidden compound very 
materially reduced the percentage of amplifiers 
rejected for change in sensitivity after potting. 

6 4 NOSE ASSEMBLY 

Other chapters of this report have covered 
the evolution of a satisfactory design for the 
vane bearing and rotating system used on the 
majority of fuzes. Attention is particularly 
called to Section 4.3.2. 

Production difficulties with the nose assem- 
bly centered principally around the problem of 


obtaining satisfactory bearings for the vane 
shaft. Early attempts to use porous bronze 
sleeve bearings proved unsatisfactory because 
of the high rotational speeds encountered in 
service. Figure 15 of Chapter 4 shows the type 
of bearing used on the first fuzes placed in pro- 
duction. Figure 18B of the same chapter shows 
the bearing in cross section. As can be seen in 
these figures, the nose bearing somewhat re- 
sembled a bicycle wheel bearing. A steel sleeve 
bearing having recesses at both ends was 
molded into the plastic nose. Staked to the 
metal propeller or molded as an insert in the 
plastic propeller was a shaft having a hardened 
conical surface at the vane end and a thread on 
the other end. On this threaded portion was 
placed a nut having a hardened conical surface 
similar to the one on the vane shaft. The bear- 
ing surfaces of the shaft and nut were selec- 
tively hardened by stopping off the unhardened 
portion by copper plating. This plating in- 
hibited the action of the cyanide case harden- 
ing solution. Steel balls were placed in the re- 
cessed ends of the bearing sleeve and contacted 
two sides of the recess and the above-mentioned 
conical surfaces. 

In production, simple fixtures were used to 
place a predetermined number of balls in each 
race, and the nut was tightened up by hand 
until the feel of the bearing was slightly looser 
than the desired end condition. The assembly 
was then placed upside down in a staking fix- 
ture, shown in Figure 21. This fixture was 
built from a conventional arbor press and 
serves to guide a hardened tool having two 
sharp projections down into the slotted vane 
lock nut, where these projections shear and 
force two tabs of metal from the shaft into a 
smaller transverse slot in the nut, thus keying 
the shaft securely to the nut and acting as a 
means for transferring torque and preventing 
backing off or loosening of the nut. Since there 
was inevitably some play between the threads 
on the shaft and the nut, this staking operation 
also forced the nut farther down on the shaft 
until all play in the threads was eliminated. 

The whole trick of this staking operation was 
to get the desired degree of tightness or pre- 
loading for the bearing without indenting the 
soft races in the steel insert sleeve. On the side 


266 


PRODUCTION 


of the ram (see Figure 21) is an eccentric stop 
nut which limits the downward motion of the 
ram and consequently the pressure applied by 
the spring to the staking tool. On the first try, 
this stop nut was set at some arbitrary mini- 
mum position and the ram advanced until lim- 
ited by the stop. The nose assembly was then 
removed from the fixture and the operator 
judged the feel of the bearings by manually ro- 
tating the propeller. Based upon experience, 
this feel gave an indication of how the stop nut 
should be adjusted for the next stroke. By this 
method, a satisfactory bearing was usually 
obtained in not over three adjustments, with 
rejects due to overshooting the desired pres- 
sure not over 4 per cent. A reasonably intelli- 
gent operator could be trained for this opera- 
tion in a day. 

Associated with the above bearing design was 
a coupling shaft whose limitations have been 
outlined in Chapter 4. The design of the rotating 
system was probably the best possible in view 
of the necessity of using something other than 
commercial ball-bearings, which were not 
available in the quantities needed for the pro- 
gram at the time fuze production was started. 
When commercial bearings became available, 
it was possible to change to a design which is 
illustrated in Figure 16, Chapter 4. In this de- 
sign, the shaft extending back to the generator 
was integral with the vane. There was enough 
play in the commercial bearing to allow for 
small angular misalignment between the gen- 
erator shaft and the nose. The bearing was 
dropped into place in the recess provided in 
the metal insert molded in the plastic nose and 
held in place by either staking or rolling over 
the edge of the recess. There was no fitting of 
bearings or variation in the tightness of the 
bearings caused by human judgment. 

It was necessary, in order to reduce vibra- 
tion, to balance the vane dynamically. The 
equipment for doing this is described in detail 
in Section 4.6. All quantity manufacturers used 
equipment basically the same as the laboratory 
setup described in that chapter. Some of them 
experimented with different types of trans- 
ducers in order to get away from the limita- 
tions of the displacement-type crystal pickups 
used in the first design, which proved unsatis- 


factory in service. Aside from erratic behavior, 
the pickup acted as a microphone and the out- 
put arising from its operation as such some- 
times interfered with the voltage generated in 
the pickup by the vibration under investiga- 
tion. At least one manufacturer used a dynamic 
pickup in conjunction with a simple RC net- 
work to convert the output, normally propor- 
tional to velocity, to a value proportional to 
displacement. This same manufacturer also ex- 
perimented with a very rigid (high resonant 
frequency) nose mount in the balancing fixture 
instead of the low-period flexible mount de- 
scribed in Chapter 7. 

After the approximate amount of the unbal- 
ance had been determined, together with the 
angular relationship of the heavy point to a 
fixed mark on the vane, weight was removed by 
either clipping the edges of the metal vane with 
a pair of tin snips or drilling small holes in the 
appropriate place on the plastic vane. Because 
of the greater number of discrete points at a 
maximum radius from which weight could be 
removed on the metal vane, these were very 
much easier to balance in production than the 
plastic ones. 


65 POWER SUPPLY AND ARMING 

For the purpose of discussion, the power 
supply and arming systems used on radio-type 
proximity fuzes can be divided into two general 
classifications. In one type of fuze, the power 
supply and arming system was combined in a 
separate subassembly adaptable to being farmed 
out to subcontractors and later assembled to the 
fuze head at the plant of the principal manu- 
facturer. An example of a power supply of this 
character is shown in Figure 22. In the other 
general classification, the components making 
up the power supply are distributed throughout 
the fuze assembly in such a manner as to pre- 
clude the identity of the power supply as a sepa- 
rate assembly. Examples of this type of con- 
struction are shown in Figures 23 and 24. In 
Figure 23 the generator proper and its turbine 
drive was installed below the fuze head, while 
the rectifier and filter condensers associated 
with it were distributed in various portions of 


SECRET 


POWER SUPPLY AND ARMING 


267 


the upper cavity containing the other electronic 
components. In Figure 24, the generator, with 
its driving turbine, is contained in the nose and 



Figure 22. Integral power supply (left) as re- 
ceived from outside manufacturer for assembly 
into radio proximity fuzes. Oscillator-amplifier 
assembly is shown at right. 

the rectifier and filter components in the main 
body of the fuze. 

651 Requirements 

The performance desired of a power supply 
can be easily specified in terms familiar to the 
electrical industry. No unfamiliar concepts are 
involved. The supply must deliver plate, fila- 
ment, and bias voltages which fall within speci- 



Figure 23. Power supply and arming system 
for T-82 fuzes. 


fled limits over the expected range of speed 
variation. The degree of filtering can be speci- 
fied in terms of permissible modulation of the 
plate supply. 


Likewise, the mechanical specifications are 
easily understood. The bearings must be ca- 
pable of standing high-speed operation and the 
arming system must perform its function with- 
in a given number of revolutions of the gen- 
erator shaft. 

Since the fuze has such a short operating life, 
it is permissible to overload some of the electric 
components. This is a particularly fortunate 
circumstance because the limited space avail- 
able does not permit the use of components hav- 
ing the safety factors usually specified. 



Figure 24. Mechanical parts and power supply 
for T-132. 


65,2 Procedures 

Generator Construction 

The housing used in early models of genera- 
tors were of molded Bakelite. This material 
proved to be unsatisfactory because of difficul- 
ties in maintaining the desired dimensional 
tolerances and was abandoned after unfavor- 
able pilot production experience in favor of 
either die cast or stamped and drawn frames. 
A power supply using die cast housings is 
shown in Figure 25 and one using a drawn case 
is illustrated in Figure 26. The die cast genera- 
tor housing required a relatively large amount 
on machine work on the rough casting in order 
to make it usable. The tooling designed for this 
purpose was somewhat elaborate and ingen- 
ious. In one manufacturer’s plant, four mul- 
tiple spindle drilling heads were used, each one 
equipped with a five-position indexing platform 
with provisions for rapid positioning and lock- 
ing of housings in position. The four heads per- 


268 


PRODUCTION 


formed 60 operations on each housing and pro- 
duced one completely machined generator 
frame every 90 sec. On each piece there were 
18 drilling, 27 counter-boring, 8 counter-sink- 
ing, and 12 tapping operations. 


POWER SUPPLY ASSEMBLY 




the bearing cups, which are clearly shown in 
the illustration. 

Both sleeve and ball bearings were used in 
the production model generator. The sleeve 
bearings were of sintered porous bronze. In 
order to make sure that an adequate supply of 
lubrication was available, even after long stor- 
age periods, some manufacturers used satu- 
rated wicks in connection with these sleeve 
bearings. Later, ball bearings were used when 
the supply of such bearings became adequate to 
support the heavy requirements of the fuze pro- 
duction program. These bearings make possible 
a “tighter” generator assembly, end play and 
side play being reduced to a minimum. In order 
to keep production up and costs down, most 
manufacturers used sleeve-bearing fits some- 


STATOR ROTOR REGULATION NETWORK 

Figure 25. Power supply using die cast gener- 
ator. 

The drawn shell housing was probably the 
most feasible from a production standpoint, 
and the majority of power supplies built used 
this type of construction. This type of genera- 
tor is shown, in considerable detail, in Figure 



Figure 27. Details of generator using drawn 
shell construction. 


POWER SUPPLY ASSEMBLY 



GENERATOR 


REGULATION NETWORK 



STATOR ROTOR 



* RECTIFIER FILTER 


Figure 26. Power supply using stamped and 
drawn shell for generator. 


27. The shell consists of two mating drawn 
pieces which contain within themselves all load 
holes and stator spacing and locating surfaces. 
The only machined piece used in the shell was 


what looser than was generally considered de- 
sirable. The use of ball bearings also provided 
a larger margin of safety against bearing fail- 
ure during production testing. Where ball bear- 
ings were used, cup-shaped beryllium-copper 
spring washers were used to take up end play 
and provide for slight dimensional differences. 
Since the amount of take-up varied within wide 
limits from fuze to fuze, additional shimming 
was provided by a series of punched Bakelite 
washers approximately 0.010 in. thick. 

Generator coil construction took two general 
forms, one using six bobbins, illustrated in Fig- 
ure 24, and the other a single serpentine coil 
assembly containing both plate and filament 
windings such as illustrated in Figures 26 and 
27. Two serpentine windings were used on 
some types of generators, the second winding 
passing over the opposite side of the stator 
pole. The cost of the bobbin-type winding was 




POWER SUPPLY AND ARMING 


269 


greater than the single serpentine coil. In addi- 
tion, the bobbin-type construction had several 
other disadvantages. It was necessary to pro- 
vide six molded bobbins, wind each bobbin with 
two separate windings, and interconnect the six 
in the proper manner. Compared to this, con- 
struction of the serpentine winding was rela- 
tively easy and inexpensive. The plate and fila- 
ment windings were wound one on top of the 
other in a simple collapsible wooden form. 
After removal from the form, the coils were 
taped on the same type of equipment used for 
taping small motor windings. The taped wind- 
ing was then shaped in a simple fixture 
having interleaved castellated projections 
which pressed the taped coil into the charac- 
teristic serpentine shape. The coil was then 
slightly distorted and inserted in the stator and 
expanded into position. The entire stator stack 
was then vacuum impregnated. 

The impregnation of both bobbin and serpen- 
tine-type stators was essentially the same. The 
stator assemblies were placed on a rack and 
dried in an oven at 250 F for approximately 
one-half hour. While still hot, the rack was 
immersed in a container of suitable varnish 
(Irvington Varnish and Insulation Company 
No. 9 Clear Drying Varnish). For proper pene- 
tration, it was necessary to hold this varnish at 
a specific gravity of 0.855, naphtha or benzene 
being used as a thinner. The container with the 
immersed coils was then placed in a vessel and 
evacuated to at least 25-in. mercury vacuum 
for 15 min. The vacuum was then released and 
the stator assemblies removed from the var- 
nish, placed in a centrifuge, and the excess var- 
nish extracted. The stators were then allowed 
to air-dry at room temperature. Both bobbin 
and serpentine coils were random wound. 

Generator shafts were made of stainless- 
steel ground precision finished stock, with the 
worm cut on a standard thread grinder. This 
worm was cut in one pass with a floor-to-floor 
time of approximately 8 sec. After cutting the 
worm, it was found necessary to de-burr the 
machined portion. No method of generating the 
worm was devised to get around this time- 
consuming hand operation. The shafts were 
held in the rotor insert by a knurled portion of 
the shaft. This knurling increased the diameter 


approximately 0.002 in. and provided a push 
fit of the shaft into the hole in the rotor insert. 

The Alnico rotors used were made either by 
casting or sintering the Alnico material. By far 
the larger number of generators produced em- 
ployed cast Alnico IV rotors. In early models 
of the generators, the soft steel or brass insert 
engaging the shaft was held in place in the cen- 
tral hole of the rotor by cerromatrix alloy. This 
procedure proved unsatisfactory for two rea- 
sons. First, the alloy has a very low melting 
point and sometimes loosened from the heat 
generated in the bearings by long test runs. The 
mechanical problem of centering the hole in 
the insert with respect to the outside diameter 
of the rotor was solved after some trouble by 
holding the outside diameter of the rotor and 
the inside diameter of the bushing in a con- 
centric collet-type fixture while the cerro- 
matrix was poured in the space between the 
rotor and hub. This method of holding hub was 
abandoned later in favor of a solid soft steel 
insert cast in the center of the Alnico rotor. 
The cast blanks were next ground so as to have 
the two sides parallel and to the proper dimen- 
sions. These blanks were then centerless 
ground to the proper outside diameter, after 
which they were placed in a collet-type chuck 
and the shaft hole drilled and reamed to the 
proper size. 

Some trouble was experienced in the begin- 
ning of production with inability of the rotors 
to stand high rotational speed. The manufac- 
turers of the rotors solved this problem so suc- 
cessfully that rotor breakage from this cause 
was practically unknown toward the end of 
the production program. 

It was at first thought that rotors could be 
held so close to the proper dimensions by the 
sintering method of manufacture that some of 
the grinding and sizing operations could be 
eliminated. This, however, proved not to be the 
case. 

The rotors were magnetized in several dif- 
ferent ways. Practically all manufacturers used 
a fixture having six retractable pole pieces 
around each of which was wound the magnetiz- 
ing coil connected in such a manner as to pro- 
vide opposite magnetic polarity to adjacent 
poles. Some manufacturers advanced and with- 


270 


PRODUCTION 


drew the pole pieces with all cams actuated 
simultaneously by one handle. Other manufac- 
turers used a fixture in which each pole was 
attached to the piston of a small air cylinder 
with the pole pieces advancing with air pres- 
sure and withdrawing through the action of a 
spring built into the cylinder assembly. Figure 
28 shows a fixture of this type. Some manufac- 
turers magnetized rotors using a bank of stor- 
age batteries as a high-amperage low-voltage 
source. Considerable difficulty was had with the 
electric contacts because of the large currents 
they were required to pass. A more satisfactory 
method of doing the job was worked out by 
some manufacturers who charged a bank of con- 
densers to approximately 300 to 400 v using a 
small receiver-type power supply to furnish the 
charging current. These condensers, having a 
total capacity of several hundred microfarads, 
were then discharged instantaneously through 
the magnetizing coils. A grid-controlled gas- 
eous discharge tube was used to trigger the dis- 
charge and by its unilateral conduction prevent 
oscillation. Another manufacturer used a fix- 
ture employing somewhat the same idea as the 
one just discussed but discharging the con- 
densers through the primary of a step-down 
transformer having a secondary of a very few 
turns which was coupled to single-turn mag- 
netizing coils made of heavy copper strap. All 
these devices served to saturate the magnet 
material in a satisfactory manner. 

Arming System 

The mechanical construction of the arming 
system employed in various production fuzes 
have been adequately covered in Chapter 4. 
Since no particularly new procedures were in- 
volved in the construction of these components, 
no discussion of them is considered necessary in 
this chapter. 

Electric Components 

The electric components in a power supply 
consist of filter and regulating condensers, re- 
sistors and the selenium rectifier assembly. The 
resistors used were standard commercial items, 
and as mentioned previously all were operated 
under conditions where the rated dissipation 
was exceeded. The resistor in the regulating 


network normally rated at x /± watt was called 
on to handle in some instances as much as 3 
watts for the short operating time of the fuze. 

The filter condensers used in a majority of 
the fuzes were specially designed and some diffi- 
culty was experienced at the beginning of the 
production program in obtaining a satisfactory 
product. The condensers were built around a 
hollow tube through which the slow-speed shaft 



Figure 28. Typical fixture for magnetizing 
rotors in generator power supplies (Globe- 
Union, Inc., photograph). 


passed. Two types of construction were em- 
ployed. One type employed a simple construc- 
tion in which condenser sections manufactured 
in the conventional manner were dropped in 
place between two concentric cardboard tubes. 
These sections were then interconnected and 
the whole assembly potted. Since there were 
voids between the condenser sections, this was 
not the most effective way to utilize the space 
available. Nevertheless, the first manufacturers 
contacted felt that this design was more fea- 
sible from a production standpoint than the 
second type to be described. In this second type 
of construction, later used by all manufac- 
turers, the two filter sections and the regulat- 
ing condenser were all wound in one operation, 
the leads being brought out by means of tabs 
laid between turns. While the working voltage 
of the condensers was only 150 volts, the test 
voltage was 300 volts. This necessitated a two- 
paper construction. Manufacturers, however, 
were able to build into the space available suffi- 
cient capacity for the purpose. 


"SECRET 



POWER SUPPLY AND ARMING 


271 


In fuzes where the filter and regulating con- 
densers were in the main body of the fuze in- 
stead of a separate power supply, small sections 
of conventional construction were employed. 
One fuze used a hermetically sealed oil-filled 
unit. 

In the early developmental stages, it was pro- 
posed to use copper oxide rectifiers primarily 
because small buttons of a suitable size were 
already available and no new techniques had 
to be devised to produce a size suitable for the 
fuze. Because of the unsatisfactory temperature 
characteristics of copper oxide rectifiers, these 
were soon discarded in favor of selenium rec- 
tifiers. When first approached on the proposi- 
tion of producing a rectifier suitable for fuze 
applications, the manufacturer, who at that 
time was the largest producer of such devices, 
expressed considerable doubt as to whether a 
selenium rectifier button could be produced in 
the size required. Selenium rectifier elements 
had never before been produced in anywhere 
near the quantity under discussion. 

At the time, all selenium rectifiers were made 
with a central hole through the disk for a 
mounting stud which held the stack in compres- 
sion. Engineers at the Bureau of Standards 
proposed a wholly novel type of construction 
which was immediately adopted and placed in 
quantity production. As can be seen from Fig- 
ure 29, there is no center hole in the disk. The 
active area of the disk is the center depressed 
area. Contact to this active area is by means of 
a low melting point metal coating sprayed so 
that it extends up the side of the depression 
and overlaps the top to a distance of approxi- 
mately y 16 of an inch. This overlapping area 
contacts the base metal of the next disk. The 
whole assembly is contained in a suitable holder 
under compression from a small spring which 
applies approximately 6-lb pressure. 

The manufacturer first approached as a sup- 
plier for these rectifier disks deserves consider- 
able credit for the development of the manufac- 
turing process and the clever tooling worked 
out. The method of manufacture and tooling 
was adopted with some modifications by the 
other manufacturers engaged in the produc- 
tion program. 

In the production of the rectifier disks a 


sheet of a base metal was first sand-blasted or 
chemically treated to provide a surface to which 
the selenium would adhere. These sheets, each 
one large enough for approximately 100 recti- 
fier buttons, were then punched out in such a 
manner that the portion which eventually be- 
came the button was projected halfway through 
the metal. At the same time, register holes 
were punched for aligning the plate in the 
fixtures subsequently used. The plate was then 
covered with a mask which left visible only the 
upraised round portions and selenium powder 
applied to the exposed surfaces. The plate was 
then placed in an oven and heat-treated to 
change the powdered selenium to a suitable 
form. Various manufacturers used different 
procedures for this step in the manufacture of 
rectifiers. In most cases it was considered a 
trade secret which they preferred not to dis- 
cuss. After the above treatment, the plates were 
placed in another fixture and a covering of 
paper cemented to the tops of the buttons. In 
the paper there was a hole which registered 
exactly in the center of each button. Over this 
another mask was placed which contained a 
slightly larger hole. A low melting point alloy 
similar to Wood’s metal was then sprayed over 
the top of the masks. This metal formed the 
conducting medium contacting the center of the 
selenium button and extending up the sides 
of the recess and overlapping the edges. 

After spraying, the mask was removed and 
the plate transferred to a fixture containing 
a multiplicity of small plungers, each one con- 
tacting the small area of counterelectrode ma- 
terial for a disk. In series with each plunger 
was a resistor serving to limit the current flow- 
ing to the button during the electroforming 
process. As the resistance of the button was 
built up during the formation of the barrier 
layer, the voltage drop across the button be- 
came higher and higher until the desired re- 
verse current resistance was attained. After 
electroforming, the plate was placed in an accu- 
rately registered die and all the buttons 
punched out of the plate in the finished form 
shown in Figure 29. 

Another supplier of rectifiers used a method 
of manufacture which resulted in a superior 
end product, particularly with respect to uni- 


SECRET 


272 


PRODUCTION 


formity. Deposition of the selenium on the base 
metal was accomplished by evaporation in a 
high vacuum and subsequent curing at the 
proper temperature to obtain the desired crys- 
talline form. Plates of base metal large enough 
for about 100 rectifier disks were processed in 
the evaporation chamber. They were then cov- 
ered with a mask of high-quality paper per- 
forated with small holes to outline the actual 
areas, the paper being held in place with a 


rectifiers and tested as a complete assembly. In 
the early days, considerable trouble was had 
with defective buttons made by the first process 
described. Figures 30 and 31 show some typical 
defects. The illustrations are self-explanatory. 

Contact to the buttons was effected by means 
of small metal tabs or flags interleaved between 
buttons and projecting through the sides of the 
case. One manufacturer used small coiled wire 
forms for this purpose in place of flags. 



Figure 29. Rectifier assembly using selenium disks. 


coating of thermosetting plastic. A counter- 
electrode material similar to that previously 
mentioned was sprayed over the entire area of 
the disks by using a skeleton of a previous 
punching operation as a mask. By extending 
the counterelectrode material over the whole 
surface of the paper, the contacts between 
adjacent disks in the finished rectifiers were 
maintained continuously during severe shock 
and vibration. The problem of microphonics in 
rectifiers was resolved by this expedient. 

The buttons were assembled into completed 


66 MISCELLANEOUS PRODUCTION 
TECHNIQUES 

As was to be expected, each manufacturer 
used techniques which had proved most desir- 
able in his experience in the manufacture of 
other electronic equipment (radio receivers in 
most cases). Some manufacturers presented 
the smaller assemblies to a fixed soldering iron 
while others kept the units in a holding fixture 
and applied the soldering iron to the work. 
Each method has its own advantages and dis- 







MISCELLANEOUS PRODUCTION TECHNIQUES 


273 


advantages and just which is best depends on 
the nature of the operation. 

Considerable difficulty was had in obtaining 
solder having high tin content due to the scar- 
city of this metal. As a result, some manufac- 
turers were forced to use low tin alloys which 
made the soldering operation somewhat more 
difficult. Actually, a solder having 63 per cent 
tin and 37 per cent lead has the lowest melting 


tin introduces problems in obtaining properly 
soldered joints. 

Most solder specifications are written to 
allow a ±5 per cent variation in the percentage 
of tin used. Since tin was not only expensive 
but scarce during World War II, most of the 
40-60 solders used actually had less than 40 per 
cent tin content. This necessitated the use of 
more heat on soldered joints, with the added 



GOOD CELL PARTIAL RING 



OFF CENTER BURNED 
RING 




THIN 

RING 


O 

WASHER 

DEFECT 


Figure 30. Typical defects in selenium rectifier disks. 


point of any lead-tin alloy, 183 C. The plastic 
range, i.e., the range of temperature in which 
the solder is in molten form, is also shortest 
with this alloy as is to be expected. The follow- 
ing tabulation shows the melting point and 
plastic range of various solder alloys. 


Tin-Lead 

Melting point 
(degrees 
centigrade) 

Plastic range 
(degrees 
centigrade) 

40-60 

265 

82 

45-55 

252 

60 

50-50 

239 

55 

55-45 

223 

39 

60-40 

202 

19 

63-37 

183 

<5 

70-30 

195 

11 


In normal times, most manufacturers prefer 
to use a solder having at least 50 per cent tin 
and some insist on a 60 per cent tin alloy. The 
necessity of using alloys of 35 and 40 per cent 


bad effects on resistors and condensers. There 
was also considerable danger that the leads 
might be displaced while the solder was taking 
such a long time to reach a solid state. The use 
of high tin content solders is particularly de- 
sirable when soldering to metal parts embedded 
in thermoplastic materials. 

Another particularly troublesome point was 
the poorly tinned lead wires on the resistors 
of some manufacturers. Resistors were often 
received with a waxy gum on the leads that 
made soldering to them particularly difficult. 
No really satisfactory method of cleaning this 
material from the resistors was evolved. 

It is interesting to note the various methods 
used by different manufacturers in handling 
fuzes along a production line, particularly after 
the oscillator and amplifier assemblies had been 
combined. Some manufacturers placed the fuze 








274 


PRODUCTION 



MANUFACTURER I MANUFACTURER I MANUFACTURER 
A I B I C 


UNVARNISHED I VARNISHED 


GOOD CELL | v ] 
INSUFFICIENT ALLOY | 
EXCESSIVE ALLOY | / • ; 

BURNED | ■ [ 

OFF CENTER| J 

DEFECTIVE WASHER I 
TOO LARGE 1 :^f|gl§| 

HIGH RIM | * 

NO WASHER OR ALLOY if 


ASSEMBLY WITH BEADS 


CELLS FROM 
ASSEMBLIES 
SHOWING BEADS 


Figure 31. Typical defects in selenium rectifier disks from three different manufacturers. 




PRODUCTION TESTING 


275 


in a simple wooden fixture which was passed on 
by hand to the next operator. Others used a 
trough in which the whole fixture was a sliding 
fit. The operator would remove the fixture 
from the trough, perform the necessary opera- 
tion, replace the fixture in the trough, and 
shove it on to the next operator. A portion of 



Figure 32. Assembly line for oscillator units. 
Oscillators are moved along trough shown on left 
side of photograph (Emerson photograph). 


an oscillator assembly line is shown in Figure 32 
with the trough used to pass on assemblies 
shown at the left. Another used a conveyor belt 
slowly moving along in front of each position. 
To this conveyor belt was fastened a fixture 
holding the unit. The operators were required 
to perform the operation while the units were 
on the move, so to speak. Overhead conveyors 
were also used. Figure 33 shows such a system 
feeding finished units to a final test area in the 
plant of one manufacturer. Figure 34 gives a 
close-up of a final test position showing the 
small pockets attached to the belt in which the 
fuzes were held. 


6 7 PRODUCTION TESTING 

The design of test equipment for proximity 
fuzes is covered in Chapter 7 of this report. 
Test equipment development for the fuze pro- 
gram was the responsibility of the Central 
Laboratory of Division 4 at the National 
Bureau of Standards [NBS]. Since the speci- 
fications for the fuze were written around tests 


performed on equipment of NBS design, most 
manufacturers followed the NBS designs in 
the construction of production test equipment. 

More testing was done in pilot production 
than was deemed necessary or desirable in 
quantity production. Not only were more tests 
conducted, but it was necessary to record in 
considerable detail data on the performance of 
every unit in order that the known characteris- 
tics of fuzes might be correlated with subse- 
quent performance of the unit in field tests. 
However, when meters have to be read to an 
exact value and perhaps recorded, the process 
takes more time than would be feasible in mass 
production. For production purposes, prac- 
tically all indicating instruments can be marked 
with go and no-go limits and fuzes tested in 
a very short time. 

In most cases manufacturers followed a test 
schedule similar to the following. Oscillator 
assemblies after completion were tested for 
(1) carrier frequency, (2) diode voltage (in 
the case of oscillator-diode [OD] units), and 
(3) grid voltage (in the case of reaction grid 



Figure 33. Assembly line for radio proximity 
fuzes showing overhead conveyor for moving com- 
pleted fuzes to final test position (Emerson 
photograph) . 

detector [RGD] units). Amplifier assemblies 
were given a preliminary test after construc- 
tion, principally to see if the circuit was func- 
tioning. After interconnecting the oscillator 
and amplifier assemblies and before potting, a 
rather complete check was made on the com- 
bined “head,” the following information- being 


EGRET 


276 


PRODUCTION 


noted on each unit: (1) millivolts (input to 
amplifier) to fire (the thyratron) at the peak 
audio frequency, (2) millivolts to fire at two 
frequencies spaced from the design center fre- 
quency in such a way as to serve as an indica- 
tion of the shaping of the amplifier, (3) peak 
audio frequency, (4) oscillator frequency, and 
(5) diode or grid voltage. 

After potting, most manufacturers tested the 
fuze head to determine whether or not any sig- 


loads. They were also checked to observe volt- 
age regulation (of the power supply) over a 
specified speed range. Most manufacturers used 
an oscilloscope connected across the high- 
voltage output which served in some instances 
as a visual indication of erratic behavior which 
would not otherwise have been detected. 

In the minds of some manufacturers was a 
well-defined suspicion that power supplies were 
a source of noise and several manufacturers 



Figure 34. Final test position on production line. Fuzes are shown arriving at position via overhead 
conveyor belt (Emerson photograph). 


nificant changes had taken place because of 
potting. In some cases, this test was abandoned 
after experience had shown that the number of 
units rejected at this test position was negli- 
gible. 

Power supplies made by outside suppliers 
were given an incoming inspection at the plant 
of the principal contractor, even though the 
unit had been checked as satisfactory by the 
original manufacturer. Units were checked for 
A voltage, B voltage, and C voltage at rated 


had under way at the end of the production 
program the design of equipment intended to 
segregate these noisy power supplies. Most of 
these devices took the form of a transient de- 
tector built around conventional thyratron cir- 
cuits, a noisy unit being indicated by either a 
visual or audible signal. 

The final acceptance test given completed 
fuzes was most complete. The acceptance or 
rejection of the unit was based on measure- 
ments of the following values: (1) carrier fre- 



PRODUCTION ACHIEVEMENT 


277 


quency, (2) diode voltage or grid voltage, de- 
pending on the type of unit, (3) millivolts to 
fire at peak audio frequency, (4) peak audio 
frequency, (5) A voltage, (6) B voltage, (7) C 
voltage, and (8) effective critical voltage of 
the thyratron. 

The last criterion (effective critical voltage) 
was determined by establishing a fixed bias on 
the thyratron grid by means of the special cir- 
cuits described in detail in Chapter 7 and run- 
ning the unit over a specified range of speeds. 
If the unit fired during this run, the bias volt- 
age was raised a fixed increment and the speed 
run repeated. Units which required a holding 
voltage greater than a specified value to prevent 
firing over the established speed range were 
rejected for noise. 

Most manufacturers maintained a rework 
department staffed by technicians familiar 
with the operation and circuits of the fuzes and 
various subassemblies. Subassemblies or com- 
pleted units rejected at the various test posi- 
tions were shunted to this rework department, 
diagnosed, and repaired if the repair job was 
deemed to be economically feasible. 

The apparatus used at the various test posi- 
tions varied in slight details from manufac- 
turer to manufacturer, although basically the 
circuit arrangements were the same. Some 
manufacturers went the limit in designing in- 
genious holding and connecting fixtures to ex- 
pedite testing. Much use was made of air 
clamping devices and multiple contact fixtures 
wherein all connections were made to a fuze or 


power supply simply by depressing one lever. 
It is a well-known fact that no tool and fixture 
designer likes to copy completely the design 
used in another plant, and as a consequence the 
variations in methods of accomplishing the 
same end result were very interesting to ob- 
serve. Since the design of holding fixtures and 
the like for fuze production presents no prob- 
lems that have not been met in the manufacture 
of other electronic equipment, a complete de- 
scription of the devices does not seem to be in 
order. 


PRODUCTION ACHIEVEMENT 


The following information, taken from re- 
ports from some of the major manufacturers 
involved, shows the magnitude of the production 
achieved. 


Manu- 

facturer* 

A 

B 

C 


Total fuzes 
produced 
315,000 
247,138 
255,996 


Number of 
Rate per month production 


at peak of 
operations 
52,800 
40,418 
39,600 


employees 

involved 

1,050 

883 

1,000-1,800 


* Manufacturer A made the complete fuze in the plant, including 
the power supply. Manufacturers B and C bought power supplies 
from outside sources. 


Figures are available from only one manu- 
facturer of power supply assemblies. They 
show a total of 490,150 power supplies made 
with production reaching a peak of 60,000 per 
month with 350 production employees. 


SECRET 


Chapter 7 

LABORATORY TESTING OF FUZES* 


71 INTRODUCTION 

F or the purpose of expediting design engi- 
neering and production control, laboratory 
tests were required to obtain pertinent per- 
formance data. These tests and associated 
equipment are described in detail in this chap- 
ter. 

The general outline of preceding chapters in 
which the principal performance characteris- 
tics and production problems were discussed 
will be followed in this chapter. A description 
of tests on the radio- and audio-frequency sec- 
tions will be followed by a discussion of tests 
on components and other relevant tests. In 
addition, a brief outline of the tests used in a 
typical quality control laboratory, and an out- 
line of tests used in a typical pilot line are in- 
cluded. As will be noted, the quality control 
test line is in general the reverse of the pilot 
line. This is obvious in that a quality control 
laboratory receives a completely assembled 
fuze, while a production line starts with com- 
ponents and ends up with a completely assem- 
bled fuze. 

The emphasis of this chapter will be on the 
general principles involved while testing, omit- 
ting the theoretical discussion, since this is 
covered in Chapters 2 and 3. It should be 
pointed out that Chapters 2, 3, and 4 also in- 
clude discussion of tests not mentioned here 
because such tests were related to development 
problems rather than the testing of finished 
fuzes. 

The preferred laboratory testing procedure 
was to evaluate the performance of the sepa- 
rate sections of the fuze, i.e., r-f, audio, detona- 
tor circuit, and power supply, rather than to 
attempt to devise an overall performance test. 
The reasons for this approach were as follows : 
Fuze failure can occur from inferior or sub- 
standard performance from any of the various 
sections of the fuze. Testing each section sepa- 

a This chapter was prepared by Thomas C. Bagg and 
Paul J. Martin of the Ordnance Development Division 
of the National Bureau of Standards. 


rately for conformance to requirements insured 
reasonably good performance for the complete 
fuze. If overall tests were used, inferior per- 
formance of one section might be compensated, 
and hence masked by extra sensitive perform- 
ance of another section. For example, a fuze 
which has an insensitive r-f section and a high- 
gain amplifier will fire the thyratron with a 
normal signal, since one section compensates 
for the other. If a section is unusually sensitive, 
the fuze may tend to become unstable and hence 
the probability for malfunctions of the fuze is 
greatly increased by a part which is out of tol- 
erance. 

Numerous attempts were made to devise an 
overall test but none of them appeared to offer 
the same assurance that fuzes would perform 
as reliably in the field as when the individual 
sections of the fuze were tested. 

In designing test equipment, there were cer- 
tain practical considerations to be taken into 
account. From the standpoint of production, 
equipment had to be designed to provide a 
maximum of economy in time, effort, and ma- 
terials, yet give the required accuracy and ease 
of operation. The length of time the unit or sub- 
assembly was under test had to be as short as 
possible to conserve the life of component 
parts, such as tubes, bearings, and gear trains. 
Accuracy of the meters and other indicators 
of the test equipment had to be kept as high 
as possible by frequent calibration against suit- 
able standards and adequate compensation for 
humidity and temperature variations. 

7 2 TESTS ON THE R-F SECTION 
7,2,1 Measurements Required 

There are three kinds of r-f assemblies to be 
tested: oscillator diode [OD], reaction grid de- 
tector [RGD], and power oscillating detector 
[POD]. The parameters which determine the 
performance of these assemblies are diode volt- 
age (for oscillator-diode units only), oscillator 


se 


SECRET 


i 


278 


TESTS ON THE R-F SECTION 


279 


grid voltage, plate current, and carrier fre- 
quency. 

As shown in Chapter 3, these parameters 
vary because of variations in radiation resist- 
ance upon approach to the target. However, 
certain of these parameter variations are more 


tions of loading and supply voltages, since in- 
stability will produce a malfunction. 

The preceding statements apply to measure- 
ments on the r-f subassembly. When measure- 
ments were made on the completed fuzes, it was 
necessary to have the r-f section operate under 
proper conditions of loading. The methods by 
which these conditions were obtained in the 
final test position are also discussed here. 


Loading Requirements 

The load presented to a fuze is composed of 
resistive and reactive components which are 
dependent upon the dimensions of the missile 
and the frequency of the oscillator. The radio 
frequency used is that which will give the re- 
quired sensitivity and stability of the fuze for 
the missile or missiles on which it is to be used. 



Figure 1 . Reference vehicles for testing prox- 
imity fuzes. These represent, from left to right, 
M-30 bomb, M-64 bomb, and 5-in. AR rocket. 

significant for each fuze type, that is, diode 
voltage for diode detectors, oscillator grid volt- 
age for reaction grid detectors, and plate cur- 
rent for power oscillating detectors. It should 
be remembered, however, that all these param- 
eters and carrier frequency are interrelated. 
It is therefore necessary to measure not only 
the steady-state values of these parameters but 
also the rate of change with load of the signifi- 
cant parameter for each fuze type. Such a 
measurement is an indication of the r-f sensi- 
tivity. Further, this section must be checked for 
stability when operating under extreme condi- 


Figure 2. Final test chamber for ring-type 
fuzes. 

Since it is inconvenient to measure the param- 
eters which determine performance on actual 
missiles in free space, some form of laboratory 
test equipment had to be designed which would 
give accurate values of these parameters under 
simulated operating conditions. 

To insure proper operation, free-space load- 
ing conditions were used as the basis, or refer- 
ence point, for all laboratory measurements. 
As pointed out in Chapters 2 and 3, there was 
an optimum frequency for each missile which 
would give the required sensitivity, but, since 



SECRET 



280 


LABORATORY TESTING OF FUZES 


most of the fuzes had to operate on more than 
one missile, a compromise on frequency was 
made and a typical, or reference, missile chosen 
for test purposes. The following table gives 
the reference missile chosen for each fuze 
type. 15, 16, 39 


Class of 
projectile 
Bomb 
Bomb 

Aircraft 

rocket 

Aircraft 

rocket 

Mortar 


Frequency, fuze type 

Brown frequency, ring-type 
White frequency, ring-type and 
all bar-type fuzes 
Brown frequency, ring-type 
and miniature rocket fuzes 
T-5 and T-6 

All-frequency mortar fuzes 


Reference 

missile 

M-30 

M-64 

5-in. AR 


M-9 

M-43C 


For convenience in calibrating laboratory 
equipment, mockups of the missile which could 


load because under light loading unstable units 
were more readily detected. 

In OD units, the reactive component of the 
load, however, had to duplicate that of free 
space, since any reactive load across the an- 
tenna not only changed the value of the param- 
eters 14 but changed the operating point of the 
oscillator (or diode circuit) in such a manner 
as to reduce the r-f sensitivity. For example, 
1 ^f of additional capacity across the nose cap 
of a diode detector-type fuze reduced the volt- 
age by about 8 per cent, resulting in a reduc- 
tion in sensitivity of approximately 16 per cent. 
The reactive component of the load was not 
critical in RGD units (see Sections 3.1.1 and 
3.1.2). 



Figure 3. Compensated loading resistor on ring- 
type fuze. 


be easily suspended in free space were made 
containing batteries and meters (see Figure 1). 

To simplify testing further and to facilitate 
correlation of the equipment in the various 
laboratories, a load resistance was chosen to 
represent approximately the free-space load 
(see Section 2.7). 3,20 The value chosen repre- 
sented a slightly lighter load than the free-space 


7 2 3 Shielding 

In order to prevent interaction between fuzes 
or the influence of nearby objects in the radia- 
tion field, it was necessary to shield the fuze 
during tests. The type of shield used for T-5 
testing was a 16-in. plate placed behind the 
fuze in such a manner as to present the same 
capacity as the missile. 48 The important feature 
of this type of shield was that it unloaded the 
oscillator without detuning the diode circuit, 
but, on the other hand, it was not an infinite 
plane and r-f voltages were induced in adjacent 
test apparatus. 

Completely enclosing shields were used for 
testing generator-powered fuzes. The excess 
capacitance loading produced by the shield was 
neutralized by inductive compensation. 24 For 
tests on the r-f subassemblies of these fuzes, the 
shields were usually 2-ft cubical metal-lined 
boxes. For tests on the completed ring-type 
fuze, where tuning and sensitivity measure- 
ments were not made, it was found more con- 
venient to use a small but very heavy all-metal 
chamber (see Figure 2). 


72 4 Loading Devices 

Since the shield unloaded the oscillator, a re- 
sistive load was necessary to secure proper 
operating data. The dummy load developed for 


TESTS ON THE R-F SECTION 


281 


T-5 tests consisted of an Aquadag (colloidal 
suspension of carbon) line drawn on Scotch 
tape and placed across the antenna insula- 
tor. 5 * 48 A similar device was used for loading 
bar-type fuzes. This was Uskon cloth, a com- 
mercial product of 377 ohms per square, which 
was satisfactory when properly located in the 
2-ft shield box. 51 

It was found possible to obtain the required 
resistance and reactance loading by the use of 
a resistance-capacitance-inductance parallel net- 
work loosely coupled to the fuze. 49 In some in- 


quency ceramic resistor upon which was wound 
a coil whose distributed inductance and capaci- 
tance was sufficient to tune out the unwanted 
portion of capacitance introduced by the shield 
and resistor. Such a resistor is illustrated in 
Figure 3. A modification of this type of load 
was used by one manufacturer when they used 
resistance wire to wind the inductance. 

These compensated resistors provided the 
proper compensation throughout the frequency 
band used, since their reactance variations with 
frequency followed those of most fuzes and 



Figure 4. Inductively tuned load for OD ring-type fuzes. 


stances, a diode rectifier and tuning indicator 
were included. 13 When this network was tuned 
to resonance, it furnished only the resistive 
component of the load, 20 while the reactive com- 
ponent of the load was adjusted by the cou- 
pling. The position or coupling of the loading 
device relative to the fuze was determined by 
trial and error to duplicate free-space loading 
conditions. 

For use in the 2-ft shield box, an inductance 
was wound on an ultra-high-frequency resistor 
to compensate for capacity excesses introduced 
by the box and resistor. Such a compensated 
resistor 24 consisted of an IRC ultra-high-fre- 


bombs. The usable frequency range of the com- 
pensated resistor for T-30 fuzes was very nar- 
row. Because the rocket on which T-30’s were 
used was long and thin compared to bombs, its 
free-space reactance variation with frequency 
was in the opposite direction. 39 

In the final test position, measurements were 
made of the overall stability of the fuze to ran- 
dom noise. It was particularly important that 
the loading introduce no errors in the measure- 
ments. Errors could be introduced in two ways : 
(1) vibration of the load caused by high-speed 
rotation of the generator, and (2) increased 
FM noise in the oscillator due to a low LC ratio 


282 


LABORATORY TESTING OF FUZES 


in the inductive load. 17 - 45 In order to increase 
the LC ratio of the load (already low due to the 
presence of the enclosure), tuning was accom- 
plished by a variable shunt inductance rather 
than with an added variable capacitance and 
fixed inductance. Coupling to the load in the 
test chamber was first made through a ring 
which fitted around the antenna of the fuze. 
This method of coupling was replaced by a disk 
in front of the fuze in order to reduce the ca- 



Figure 5. Disk load for bar-type fuzes. Central 
tube and nozzle carries compressed air to drive 
windmill. 


pacity of the load and to reduce inductive 
coupling between the oscillator and loading 
coils 21 * 43 (see Figure 4). 

For RGD units, no variable tuning was nec- 
essary, so that the means of loading simply be- 
came a compensated resistor connected between 
the coupling disk and the chamber. 

The test fixture for bar-type fuzes was a 
2-ft shield box with the fuze mounted on a 
standoff to reduce capacity loading across the 
dipoles. The length of the standoff was impor- 
tant in that it became a resonant line at par- 


ticular frequencies, lengths, and diameters. 25 * 36 
In the 2-ft box, a 3y2-in. pipe 7 in. long gave 
no spurious effects. The load consisted of either 
a sheet of Uskon cloth alongside the dipoles 
(Figure 37 of this chapter) or a disk of Uskon 
cloth in front of the dipoles (Figure 5). The 
disk did not require orientation of the dipoles. 
To prevent contamination of the load by oil, 
sludge, etc., the cloth was covered by a thin 
sheet of Lucite or celluloid. A test chamber for 
laboratory testing of complete fuzes with trans- 
verse antennas was designed for use as a noise 
reference fixture to evaluate the production test 
boxes (Figure 6). This chamber used a tuned 
resistance load similar to that described above. 43 

Some difficulty was experienced in correlat- 
ing different test positions because of changes 
in r-f resistance with frequency. This variation 
was greatest with high-value resistors. 55 To 
overcome this difficulty a set of resistors was 
arbitrarily selected as reference standards. 

For units which had normal radiation resist- 
ances of 100,000 ohms or greater, it was found 
desirable and convenient to use no resistive 
component other than that in the tuning ele- 



Figure 6. Final test chamber for bar-type fuzes. 


ment of the load. This type of loading was used 
with T-51, T-82, T-132, and T-171 fuzes. 

Several experimental test fixtures were con- 
structed which used a quarter-wave line to ob- 
tain the r-f load. Westinghouse (Baltimore) 
used such a device for their T-5 fuzes. Philco 
also used it for their T-50 production. Some 


SECRET 




TESTS ON THE R-F SECTION 


283 


work was done at the National Bureau of Stand- 
ards on this type of loading, but not with par- 
ticularly satisfying results except in the case of 
a device for the measurement of absolute sensi- 



Figure 7. Resistor for determining sensitivity 
of bar-type fuzes. 


tivity of an end-fed axially excited fuze (see 
Section 2.12). 

Loads based on parallel transmission lines 
were also experimented with but not used to 
any great extent. 


tivity obtained from the formulas [equations 
(4) and (6), Chapter 3] 

dV 

d In R’ 


or 


s - E -(r .-‘ } 

Figures 3 and 7 illustrate loading resistors 
used in sensitivity determinations. For certain 
units where the normal load was in the linear 
portion of the loading curve (see Figure 7, 
Chapter 3), only two points, or resistors, were 
necessary to determine the sensitivity. For fuzes 
which had very high load resistance, uncom- 
pensated resistors of 100,000 ohms and infinity 
were used where [equation (16), Chapter 3] 

s = V m -V. 

It was first thought unimportant to induc- 
tively compensate sensitivity resistors for RGD 
units, 44 but it was found desirable to do so in 
order to prevent shifting of the operating point 
of the oscillator. 


Sensitivity Test 

The most direct method of measuring r-f 
sensitivity is a pole test as described in Section 
2 . 12 . 

This test was the only practical means of de- 
termining the sensitivity of very early fuzes, 
because the close coupling between the oscilla- 
tor and diode circuits would throw the oscilla- 
tor into unstable operation when the fuze was 
unloaded to obtain V m for the sensitivity for- 
mula [equation (4), Chapter 3]. 

However, for production testing, this was 
impractical and was used only as the stand- 
ard for free-space loading and absolute sensi- 
tivity measurements. 

The use of compensated resistors in the 2-ft 
shield box gave rapid and sufficiently accurate 
data for sensitivity determinations. For such 
determinations, the diode voltage, grid voltage, 
or plate current was plotted against the natural 
logarithm of the load resistance and the sensi- 


726 Stability Test 

In order to test fuzes for r-f stability, the 
first test used for T-5 fuzes 5 consisted of de- 
creasing the r-f loading and tuning the unit 
through resonance. If no discontinuities were 
observed in diode voltage, plate current, or 
carrier frequency, the fuze was considered 
stable. Other indications of instability were 
self -blocking (squegging) 5 which was noted by 
the presence of discrete side bands. A more 
satisfactory stability test was devised where 
an alternating plate voltage was applied to the 
oscillator, which caused it to go in and out of 
oscillation. The plate voltage was applied to 
the horizontal plates of an oscilloscope, while 
the oscillator grid voltage was applied to the 
vertical plates ; this showed the grid voltage as 
a function of plate voltage and readily dis- 
closed any tendencies toward instability. 


SECRET 


284 


LABORATORY TESTING OF FUZES 


7,2,7 Carrier Frequency 

Carrier frequencies were measured by loosely 
coupled absorption-type wavemeters or ultra- 
high-frequency receivers. Care was required 
when using superheterodyne receivers to insure 
that the true frequency was read and not that 
of the image or some other spurious responses. 
To maintain accurate calibrations, harmonics 
of a standard 5-mc oscillator were used. These 
oscillators were periodically checked against 
WWV, the standard frequency station of the 
National Bureau of Standards. 


AUDIO TESTS 


connected or blocked, the impedance which the 
amplifier saw when looking back into the oscil- 
lator would be altered and normal signals such 
as filament hum coming from the oscillator 
would be distorted. Any indicating device con- 
nected to the amplifier output, i.e., thyratron 
grid, was such that it did not affect the ampli- 
fier characteristics. A high-impedance cathode 
follower was usually used for coupling test 
instruments to the amplifier output. Any con- 
nection to the thyratron plate had to be such 
that proper voltages were applied, since the 
thyratron critical voltage was a function of its 
plate voltage. Also, any firing indicator circuits 
had to have current limiters so as not to weaken 
or destroy the thyratron. 


7,3,1 Measurements Required 

The function of the audio portion of the fuze 
is to select the proper signal and amplify it suf- 
ficiently to actuate the trigger circuit (thyra- 
tron). Laboratory tests required were there- 
fore those necessary to determine the gain- 


7 32 Input Circuits 

It was necessary to use various types of input 
circuits to meet the needs of different units. 
With oscillator-diode units, the diode was 
blocked while making amplifier measurements 
to eliminate noise developed in the oscillator. 1 


|:| ISOLATION TRANSFORMER 


AUDIO 

OSCILLATOR 



l:l ISOLATION 
TRANSFORMER 


AUDIO 

OSCILLATOR 



Figure 8. Schematic of audio input test circuits (OD, RGD, POD). 


frequency characteristic as well as the peak 
gain. Gain, as such, was not measured. Instead, 
the input signal to the amplifier (in rms milli- 
volts) required to fire the thyratron was used 
to indicate amplifier quality. Every effort was 
made to insure that test conditions were the 
same as those which existed when the fuze was 
in operation. Hence, if the oscillator were dis- 


This was easily done by applying a negative 
voltage to the diode and amplifier test lead. This 
voltage had to be greater than the peak r-f 
voltage developed in the diode circuit to com- 
pensate for the rise in r-f voltage occurring 
when the diode was blocked and made non- 
conducting. Blocking the diode changed the 
impedance which the amplifier saw when look- 


AUDIO TESTS 


285 


in g back toward the oscillator. 41 To correct for 
this change of impedance, a resistor of 170,000 
ohms was used in series with the blocking bat- 
tery 46 and source of audio voltage. This audio 
voltage was obtained from a commercial audio 
oscillator through a voltage divider in order 
to permit metering of the voltage by rectifier- 
type voltmeters. Typical audio input circuits 
are shown in Figure 8. 



Figure 9. Schematic of cathode follower and 
d-c VTVM (used on amplifier output) . 


For testing fuzes which contained no diode, 
the r-f signals were eliminated by either dis- 
connecting the oscillator from the amplifier 
(which in some instances was inconvenient) or 
using a low-impedance by-pass between the 
oscillator and high-input impedance amplifier. 19 
In the case of choke 51 or transformer input, it 
was necessary to use the first method and ob- 
tain the audio voltage through a circuit equiva- 
lent to the fuze oscillator. 

As pointed out previously, the filament hum 
present in the oscillator output due to an un- 
balanced filament supply had to be duplicated 
by a voltage injected with the test signal. This 
was done by raising the voltage divider above 
ground potential by the amount of hum voltage 
necessary to duplicate that present in the oscil- 
lator output. The phase of the hum so injected 
had to be within 10 degrees of that in the oscil- 


lator output. Care to maintain the normal value 
of filament hum appearing at the thyratron 
grid was also necessary in order to obtain 
proper effective critical voltage for the thyra- 
tron (see Section 3.3.5). 10 ’ 47 


7 3 3 Output Circuits 

Since the amplifier load consisted of an RC 
network which controlled the high-frequency 
cutoff and phase of the feedback voltage, it was 



Figure 10. Cathode follower impedance chart. 
Measurement of cathode follower input imped- 
ance by use of accurate 30- and 90-megohm re- 
sistors. 

Apply a convenient voltage (10 volts, 200 c) directly to 
cathode follower input lead and observe output E\ on 
vacuum-tube voltmeter. Apply same voltage through series 
resistor of 30 megohms and note reading Eo ( 30 ) . Repeat 
foregoing step with 90-megohm resistor and note reading 
(90). Form the ratios 

Eq (30) and Eo (90) 

E i E\ 

Locate point on graph corresponding to two ratios and find 
impedance by interpolating between curves of constant 
impedance. 

essential that any test instrument connected to 
the amplifier output would in no way alter the 
amplifier output impedance. For this purpose, 
cathode followers were used for coupling to 
commercial voltage indicators, such as volt- 
meters, oscilloscopes, or magic-eye tubes. The 


| 


SECRET 


286 


LABORATORY TESTING OF FUZES 


impedance of the cathode followers used was of 
the order of 50 megohms at 200 c and 12 
megohms at 1,000 c. Values in excess of 40 
megohms at 200 c and 10 megohms at 1,000 c 
caused negligible errors in the measurements 
and these values were introduced as specifica- 
tion limits for acceptance testing. 

Impedance losses in test leads between the 
amplifier and cathode follower due to capacity 
to ground frequently caused difficulty in meet- 
ing the specification limits. By using a shielded 
lead where the shield is connected to the cath- 
ode of the follower tube, this parallel impedance 
loss can be greatly reduced (see Figure 9). 
Figure 10 illustrates a method of rapidly de- 
termining the input impedance of the follower 
when the capacitive components of the lead and 
tube are considered. 


Thyratron Tests 

Effective Critical Voltage. The highest nega- 
tive grid biasing voltage which will fire the 
thyratron is called the critical voltage. (The 
critical voltage is, of course, different for a-c 
operation of the thyratron filament than for 
d-c.) The term normal critical voltage was ap- 
plied to the highest negative biasing voltage 
which would fire the thyratron in the operating 
fuze assembly with microphonic noise from the 
oscillator blocked. The usual procedure for 
measuring normal critical voltage was to block 
the oscillator and inject (at the amplifier in- 
put) a ripple signal equivalent in magnitude 
and phase to that ripple from the oscillator 
filament. The term effective critical voltage was 
applied to the highest negative biasing voltage 
which would fire the thyratron when the fuze 
was completely operating, that is, when micro- 
phonic noise from the oscillator was passed on 
to the thyratron grid. In the generator-powered 
fuzes, these measurements were made with the 
generator running (driven by an air jet 
directed on the vanes) so that microphonics 
induced by the rotating system would show up 
as a change in the effective bias of the thyra- 
tron. 

In making measurements of effective critical 
voltage, it was not possible just to reduce the 


applied bias on the thyratron, since this bias 
was also applied (through a voltage divider) to 
the pentode. 11 Such procedure would have 
caused changes in amplification resulting in 
other-than-normal hum voltage at the thyra- 
tron grid. A high-impedance positive voltage 
source was therefore applied directly to the 
thyratron grid along with a high-impedance 
voltmeter. It was also necessary in all of the 
equipment to insure that there was very little 
coupling between input and output test circuits, 
since any such coupling would appear as paral- 
leling the gain-control condenser (C8 in Figure 


THY PLATE IOPOO OHMS 
© VVAA 


0.1 MF 



+135 V 


THY PLATE 10,000 OHMS 

© 1 VvV 

r — dr-i 


i-iY 


t^rr 

4 WATT 
NEON 


4 = 0-1 <> |.0 


ADD FOR TESTING 
RC ARMING CIRCUITS 


Figure 11. Firing indicator for thyratrons: 
for tube and unit testing, except units with RC 
arming (top) ; brighter flash, satisfactory only 
when a-c signal is used on thyratron grid 
(bottom) . 


26 of Chapter 3) and seriously affect gain ad- 
justment or amplifier performance. 

A type test (later a production test) was re- 
quired to determine if the actual bias at the 
thyratron grid was approximately equal to the 
applied C bias. Leakages through the output 
coupling condenser to the plate supply, through 
the potting compound to ground, and along the 
component surfaces, tended to reduce the bias 
at the thyratron grid. Such leakages, if present, 
caused unstable and erratic performance. 

Firing Indicator. The most convenient firing 
indicator consisted of a neon bulb and RC net- 
work where the neon fired either on discharge 


SECRET 


STABILITY TESTS 


287 


or charge of a condenser (Figure 11). Such a 
circuit was advantageous in that it was simple, 
unharmful to the thyratron, and quenched so 
quickly that the thyratron would recover for 
rapid testing. Other types of firing indicators 
were developed and used, ranging from a simple 
lock-in circuit which remained operative once 
the thyratron fired, to circuits which rang bells, 
flashed lights, etc. 

Routine tests for passing surge currents 
through the thyratron were frequently dis- 
cussed but seldom used outside the laboratory 
since the failure of a thyratron in a fuze to pass 
ample current was rarely reported. 


74 STABILITY TESTS 

7,41 Purpose of Stability Tests 

A major cause of malfunctioning of fuzes in 
field and service tests was noise or micro- 
phonics in the electronic assemblies. Accord- 
ingly, considerable effort was made to devise 
laboratory tests which would show up or sort 
out noisy units. Since noise was usually pro- 
duced by the vibration of loose or weak parts, 
either in the circuit or in the tubes, the testing 
methods employed shaking or shocking tech- 
niques. The ability of a fuze to withstand vibra- 
tion was considered as a measure of its sta- 
bility. 

Various methods were used to indicate the 
stability of a fuze under vibration: (1) the 
peak noise voltage at the thyratron grid, (2) 
the highest negative bias applied to the thyra- 
tron grid, which would cause firing, i.e., effec- 
tive critical voltage under the selected condi- 
tions of vibration, and (3) the difference be- 
tween the effective critical voltage and the 
thyratron bias voltage, i.e., noise margin. 


7,42 Methods of Producing 

Vibration or Shock 

Laboratory methods of inducing vibration 
in fuzes attempted to duplicate (in a crude 


way) the vibrations experienced by the fuze on 
a missile in flight. It is well known that air 
turbulence and fin flutter produce intensive vi- 
bration in missiles and these, of course, will be 
transmitted to the fuze. 

The first vibration or shock method employed 
to select stable fuzes was the simple expedient 
of striking the fuze (or rather a test missile in 
which it was mounted) with a club. This 
method was strictly qualitative, but field scores 
were greatly improved by discarding fuzes 
which showed excessive noise signals when hit 
with the club. 

The club test for fuze stability was refined by 
producing the shock with a calibrated pendu- 
lum and employing a standard mount for the 
fuze. 5 Although the shock test produced little 
reliable quantitative data, it did lead to consid- 
erable improvement in tube design and to im- 
provements in the technique of anchoring com- 
ponents in the r-f section. All T-5 fuzes were 
subjected to the pendulum shock test. 

With the advent of generator-powered fuzes, 
an additional source of vibrational energy 
appeared through slight unbalance of the high- 
speed rotating system. Analysis showed that 
such an unbalanced rotating system was the 
best microphonics testing device, because it 
produced exciting forces in all directions in a 
plane, because the entire range of exciting fre- 
quencies could be easily covered, and because 
the exciting forces were maintained long 
enough to build up peak amplitudes at resonant 
frequencies. 9 ’ 23 The weaknesses of the shock 
test were the presence of directional effects and 
the inability of a single shock to build up vibra- 
tion amplitudes at resonant frequencies. 

When a fuze was mounted in its adapter or 
encasing can on a bomb, unbalance in the rotat- 
ing system produced vibrations of large ampli- 
tudes because the bottom of the adapter acted 
as a resonant diaphragm in the frequency 
range of 20,000 to 35,000 rpm (see Figure 
12). This method of producing vibration was 
used in the final test fixture where an adapter 
was tightly screwed into a massive test cham- 
ber. A shoulder of at least 0.010 in. was cut 
on the bottom of the adapter to simulate mount- 
ing on a bomb ogive (see Figure 12). To per- 
mit uniform testing and to compensate for 


1ECRET 


288 


LABORATORY TESTING OF FUZES 


adapter differences, the bottoms of the adapters 
were cut so that resonance occurred at approxi- 
mately 25,000 rpm. 



C Shaft shield 

D Generator rotor (unbalanced) 

E Gear train (binding) 

F Adapter can bottom (resonant diaphragm) 
G Ogive of bomb 



A Adapter can bottom (resonant diaphragm) 
B Shoulder greater 0.010 in. 

C Test fixture 


Figure 12. Resonant mountings: fuze on bomb 
illustrating pertinent vibration elements (top) ; 
test adapter (bottom). 


Numerous difficulties were encountered in 
calibrating such a mount. A study of adapters 
showed that the mechanical properties of the 


diaphragm were not uniform. This led to dif- 
ferent amplitudes and changes in frequency 
during use, which were probably caused by cold 
working of the metal and fatigue. In addition, 
an analysis of such a resonant mount in a test 
chamber revealed numerous uncontrollable var- 
iables. 37 As a temporary expedient, an assembly 
containing a rotating system of known unbal- 
ance was used to calibrate test fixtures. Such 
assemblies were called reference vibration 
heads and are shown in Figure 13. 

As propeller balancing techniques improved, 



Figure 13. Reference vibration heads used to 

calibrate vibration response of test fixtures. 

self-excited resonant vibration systems lost 
their ability to test adequately stability and 
other methods were sought. One system pro- 
posed was the addition of a known unbalance to 
the propeller and the use of a soft mount to 
overcome the difficulties inherent in a resonant 
system. This system appeared to have a number 
of advantages for obtaining a qualitative meas- 
ure of unit stability. 37 Development of this 
method was not completed at the end of World 
War II. 

Many types of external vibrators (in con- 
trast to the internal source of vibration in the 
fuze's rotating system) were designed and 
tried. The first, the rotary vibrator (Figure 
14), followed the principle mentioned above, 
that is, an unbalanced mass was rotated at high 
speeds. 9 The vibrator housing was supported on 


SECRET 




STABILITY TESTS 


289 


a soft mount with the fuze to be tested on the 
other end. Bearing failure, poor high-speed 
motors, and the small mass which such a sys- 
tem could vibrate, limited the use of the rotary 
vibrator to components (particularly tubes), 
head assemblies, and miniature fuzes. 

Several models of a vibrator using a process- 
ing ring operated with some success (Figure 
15). One contractor turned the unbalanced tur- 
bine 90 degrees, getting vibration in a vertical 
plane. Models in which a ball was driven at 
high speed around a race showed promise 38 
(Figure 16). Another device which proved un- 
satisfactory consisted of four diaphragms 90 
degrees apart around the unit mount, the dia- 
phragms being actuated by a rotating valve on 
a high-pressure air line. The impedance of the 
air supply lines was so great that very little 
energy was delivered to the unit, and the 
scheme was also unsatisfactory at high frequen- 
cies. None of these vibrators was developed for 
production testing by the end of World War II. 



Figure 14A. Rotary vibrator. Schematic section 
of head assembly mounted on mechanically driven 
vibrators. 


7 ‘ 4 ' 3 Other Noise Sources 

In addition to noises caused by microphonics, 
there were other sources of noise in the fuze 
which had to be eliminated (see Section 3.1.5). 
In the later part of T-5 production, extremely 



Figure 14B. Miniature fuze mounted on air- 
driven vibrator; operates on principles illustrated 
in Figure 14A where air turbine is unbalanced. 




290 


LABORATORY TESTING OF FUZES 



Figure 16. Ball race vibrator. 

erties of the pentode, while the reliability of the 
detonator circuit was no better than the de- 
pendability of the thyratron. Because the tubes 
were tiny, complex, and difficult to manufac- 
ture, it was necessary to work out careful per- 
formance tests in order to insure that the 
tubes would be satisfactory. 6 * 35 > 53 Here we will 
confine the discussion primarily to a listing of 
the properties which were measured. 

As indicated in Section 7.4, one of the most 


be met in turn by setting close tolerances on the 
components. This section outlines the types of 
tests which were used to select the most im- 
portant components. Details of the tests are 
generally not given ; instead, reference is made 
to source material in the bibliography. 


752 Tube Testing 

Tubes were probably the most critical of all 
components both from performance and manu- 
facturing viewpoints. Proper performance of 
the oscillator was based primarily on the char- 
acteristics of the triode. The required response 
of the amplifier was intimately related to prop- 


sharp high-voltage pulses were observed on a 
long-persistent screen oscilloscope. Improve- 
ments in tubes and changes in operating point 
of the oscillator apparently eliminated these 
pulses and no further study was necessary. Ro- 
tational frequency noise, that is, noise associ- 
ated with the speed of the rotating system, was 
caused by eccentric coupling shafts rotating in 


Figure 15. Precessing ring vibrator. 

the r-f field, gear trains which had binding 
action at a certain spot, etc. The power supply 
was an occasional strong source of rotational 
noise, particularly when radio frequency was 
present in the generator and gear train hous- 
ing. 

7 5 COMPONENT TESTING 

Introduction 

Proper performance of the major subassem- 
blies of the fuzes depended on the careful selec- 
tion of the various components. Close toler- 
ances were set on the performance require- 
ments of the subassemblies and these could only 


COMPONENT TESTING 


291 


Table 1. Summary of diode tests. 6 * 35 


Name of test 


Limits and requirements (NDRC specifications, 
Purpose of test Aug. 1, 1944) 


Filament current* 

Leakage test* 

Self-noise test* 

Rectified current 
test* 

Centrifugef 

Operation! 


To insure that filament current will 
be within limits for satisfactory 
operation. 

To measure reverse d-c current 
through leakage paths in the tube. 

To measure a-c component of leak- 
age current mentioned above. 

To measure the diode efficiency, that 
is, the ratio of the d-c voltage de- 
veloped across a specified load to 
the peak input voltage. 

To determine ability to withstand 
setback encountered in rocket fuze 
application. 

To insure adequate life expectancy. 


Filament current shall be at least 60 ma d-c, and not 
exceed 80 ma d-c, with 0.6 v d-c applied directly to 
filament. 

Leakage current shall not be greater than 3 na d-c 
under operating conditions. 

Maximum peak self-noise shall not exceed 0.1 mv. 

Diode current shall be at least 30 n a d-c with 30 v 
rms, 60 c, input. 


To pass critical tests after acceleration of 2,500 g. 


After operation for 15 min, the rectified current shall 
not differ more than 10% from the value at 
beginning of operation. 


* These tests were given to all tubes (100% tests). 

t These tests were given to representative samples from each lot of tubes (sampling tests). 


Table 2. Summary of triode tests. 6 * 53 


Name of test 


Limits and requirements (Ordnance Dept. 
Purpose of test specification, July 25, 1945) 


Heater current* 
(filament current) 

Gas test* 


Oscillation* (grid 
bias test) 


Oscillation frequency 
testf 


Self-noisef 

Microphonics* 


Operation testf 


Centrifugef 


To insure that filament current will 
be within limits for satisfactory 
operation. 

To detect presence of gas which 
creates fluctuations of plate cur- 
rent and internal impedance. 

To insure sufficient grid bias volt- 
age can be developed to maintain 
uninterrupted oscillation. 

To insure that oscillator frequency 
controlled by interelectrode tube 
capacities will be held within 
proper limits. 

To measure spontaneous noise 
within the tube. 

To insure minimum noise voltage 
when tube is subjected to vibra- 
tion. 

To insure satisfactory oscillation 
performance after a period of 
operation in excess of the ex- 
pected time for combined testing 
of the tube and the completed 
fuze. 

To determine ability to withstand 
setback encountered in rocket and 
mortar fuze application. 


Filament current shall be between 0.230 amp d-c and 
0.150 amp d-c with applied voltage of 1.20 v d-c. 

Grid current must not exceed 2 na d-c between 1 and 
6 sec after application of test voltages. 

Grid bias of not less than 22 v d-c must be self- 
developed with plate current of between 7 and 11 
ma d-c for from 1 to 30 sec after application of 
test voltages. 

Frequency of each tube must not differ by more than 
±5 me from standardized value. 


Total instantaneous noise of tube at rest shall not 
exceed 0.01 v. 

The total instantaneous noise after amplification in 
a shaped amplifier (gain approx 100) shall not 
exceed 0.6 v when vibrated (0.012 in amplitude) 
at a frequency in the pass band of the amplifier. 

After 15-min operation under specified conditions, 
oscillator grid bias must not differ by more than 
20% from value noted prior to test. 


Grid bias and plate current must not differ by more 
than 20% from values before centrifuging, 12,000#. 


* These tests were given to all tubes (100% tests). 

t These tests were given to representative samples from each lot of tubes (sampling tests). 


292 


LABORATORY TESTING OF FUZES 


important properties, particularly for the tri- 
ode, was microphonic stability. This property 
was examined on tubes before they were built 
into fuzes. It was also examined, though in- 
directly, in stability tests on completed fuzes 
(see Section 7.4). 


check a large percentage of the resistors and 
capacitors to obtain some idea of the effect of 
component variations upon fuze performance. 
The production line, however, did not require 
such information, but did find it necessary to 
check certain critical resistors and condensers 


Table 3. Summary of pentode tests. 6 - 53 




Limits and requirements (Ordnance Dept. 


Name of test 

Purpose of test 

specification, July 25, 1945) 



Heater or filament 
current* 

Voltage amplifica- 
tion* 


To insure that filament current will 
be within limits for satisfactory 
operation. 

To insure that voltage amplification 
of pentodes is sufficient. 


Filament current shall be between 0.072 amp d-c 
maximum and 0.052 amp d-c at 0.6 v d-c. 

Voltage amplification in a specified amplifier (no 
feedback) shall not be less than 90 nor greater 
than 120. 


Noise* 

(microphonics) 


To insure that pentodes used in Total instantaneous noise, expressed as the maximum 
fuzes are not excessively micro- peak variation in the plate voltage caused by any 
phonic. single mechanical shock, shall not exceed 0.75 v 

when the tube is subjected to the proper test 
conditions. 


Dynamic input im- 
pedance! 

Plate resistance! 


To insure that input impedance is 
sufficiently great. 

To insure that plate resistance is 
sufficiently great, since low plate 
resistance affects the phase shift 
of the feedback network. 


The input impedance shall not be less than 10 
megohms under operating conditions. 

The plate resistance while the tube is operating in 
the specified circuit shall be in the range 2.0 to 
5.75 megohms. 


Special (low) volt- 
age amplification! 

Operation test! 


Mechanical stability 
of elements! 
(centrifuge test) 


Surface electric 
leakage! 


To insure that the amplifier would 
function properly with reduced 
voltages. 

To insure satisfactory voltage 
amplification of the pentode after 
a period of operation in excess of 
the expected total time required 
for testing the tube and com- 
pleted fuze. 

To determine ability to withstand 
setback encountered in rocket and 
mortar fuze application. 


To insure that surface leakage of 
the tube is not low enough to im- 
pair its operation. 


The voltage amplification when determined in the 
specified manner shall not be less than 75. 

After 15-min operation under specified conditions, 
voltage amplification must not differ by more than 
10% from value noted prior to test. 


To withstand acceleration of 12,000# under certain 
specified conditions, and 2,500# under other con- 
ditions. The value of voltage amplification after 
centrifuging shall not differ by more than 10 per 
cent of the value prior to centrifuging, and the 
noise after centrifuging shall not exceed 0.83 v 
peak. 

The minimum electric resistance between the plate 
lead and all other leads shall be 25 megohms. 


* These tests were given to all tubes ( 100% tests ) . 

t These tests were given to representative samples from each lot of tubes (sampling tests). 


A summary of the important tests on the 
various tubes is presented in Table 1 for diodes, 
Table 2 for triodes, Table 3 for pentodes, and 
Table 4 for thyratrons. 

Resistors and Capacitors 
It was necessary for pilot line production to 


to maintain a high level of fuze performance. 
When such testing was required, ordinary com- 
mercial-type limit bridges were used, although 
several automatic sorting devices were pro- 
posed and tried. Special surge testers to de- 
termine the inductance of the cylindrically 
wound detonator-firing capacitor were devel- 
oped in order to design more efficient noninduc- 



COMPONENT TESTING 


293 


Table 4. Summary of thyratron tests. 6 * 53 


Name of test 


Purpose of test 


Limits and requirements (Ordnance Dept, 
specification, July 25, 1945) 


Heater or filament 
current* 

Critical grid voltage* 


Grid circuit voltage 
drop* 


Minimum surge* 


Constancy of critical 
voltagef 

Operation test part 1, 
heater lifef 


Part 2, repeated 
surge! 


Mechanical stability 
of elements! 
(centrifuge) 


Internal electric 
leakage 

Surface electric 
leakage! 


To insure that filament current will 
be within limits for satisfactory 
operation. 

To insure that critical grid bias is 
within proper limits, since this 
parameter is one which governs 
overall sensitivity. 

To insure that there is no excessive 
leakage between the tube leads; 
such leakage tends to make the 
negative bias at the grid itself 
lower than the applied C bias. 

To insure that the minimum peak 

• discharge current passed by the 
thyratron will be sufficient to fire 
the electric detonator. 

To determine the effect of changes 
in supply voltages on the critical 
grid voltage. 

To insure that the thyratron will 
not undergo any deterioration in 
operating characteristics after a 
period in excess of the expected 
time required for testing the tube 
and completed fuze. 

To insure that critical grid voltage 
does not change appreciably after 
the thyratron has been fired ten 
successive times. 


To determine ability to withstand 
setback encountered in the rocket 
and mortar fuze application. 


To insure that electric leakage 
within the thyratron is not ex- 
cessive. 

To insure that surface electric leak- 
age about the thyratron is not 
excessive. 


Filament current shall be between 0.100 amp d-c and 
0.080 amp d-c at 1.2 v d-c. 

The critical grid voltage shall be within the range 
— 1.7 to — 2.5 v d-c. 


The grid circuit voltage drop shall not exceed 0.40 
v d-c. 


The peak plate current shall not be less than 5 amp. 


Variation in the critical grid voltage with specified 
changes in heater and plate voltages shall not 
exceed 0.6 v d-c. 

The tube shall be electrically stable as evidenced by 
freedom from changes in critical grid voltage ex- 
ceeding 0.40 v d-c after being operated for 15 min. 


The tube shall be electrically stable, as evidenced by 
repeated compliance with the minimum surge test, 
freedom from changes in critical grid voltage ex- 
ceeding 20% of initial value and from changes in 
grid circuit voltage drop exceeding 0.20 v d-c, after 
operation for 15 min. 

To withstand acceleration of 12,000# under certain 
specified conditions, and 2,500# under other condi- 
tions; after centrifuging the critical grid voltage 
shall not differ by more than 10% of pre- 
centrifuging value, the value of grid circuit volt- 
age drop shall not differ by more than 0.15 v d-c 
from the precentrifuging value, and the minimum 
surge current shall be greater than 4.5 amp. 

The thyratron shall not pass more than 2.5 na d-c 
when the control grid is tied to the plate and minus 
135 v d-c applied. 

The minimum electric resistance between the plate 
lead and all other leads shall be 25 megohms. 


* These tests were performed on all tubes (100% tests). 

t These tests were performed on representative samples from each lot of tubes (sampling tests). 


tive condensers. The reader is referred to refer- 
ence 32 for the background of component tests 
and specifications. 

7,5,4 Coil Testing 

In general, testing of oscillator coils con- 
sisted of visual inspection to insure that ade- 
quate cement had been applied and that the 
proper number of turns had been wound. How- 


ever, for transverse antenna fuzes (T-51) a 
double coil was used. This double coil had to be 
tested for high-voltage shorts or breakdowns. 
Figure 17 shows a small test set which was used 
for breakdown testing of coils and condensers. 


5 Rectifier Assemblies 

Since the rectifier buttons used in the fuzes 


' SECRET 




4 


294 


LABORATORY TESTING OF FUZES 


were developed specifically for the fuzes, new 
production test equipment was required to 
make 100 per cent tests. This equipment was 
designed to measure the forward voltage drop 
and back current under specified conditions. In 
addition, a probe was developed which would 



Figure 17. High potential leakage tester. 
Double-wound coil for T-51 fuze is shown being 
tested for insulation between coils. 

apply the proper voltages and compression or 
contact force. Requirements for rectifier test- 
ing are given in Section 3.4. 5. 33 ’ 52 


Chokes and Transformers 

The small r-f filter choke was very delicate 
by virtue of the very fine wire coil. This fine 
wire would frequently be broken while bend- 
ing the choke leads during assembly. A con- 
tinuity test was, therefore, incorporated in the 
audio prepot test position as an oscillator func- 
tioning test. The audio chokes and transform- 
ers used in certain fuzes (T-51 and T-82) were 
frequently tested before assembly in mockup 
amplifiers to determine their resonant fre- 
quency. A mockup circuit was most satisfac- 
tory, since it gave direct comparison data and 
since direct inductance measurements of these 
particular chokes were difficult. 


7.S.7 Propeller and Turbine Assemblies 

As mentioned previously, every effort to 
eliminate vibration of the fuzes was made. One 
of the largest sources of vibration energy came 
from unbalanced rotating systems. Unbalanced 
propellers and off-center coupling shafts pro- 
duced considerable vibration in the large fuzes, 
while dynamic unbalance of the turbine and 
generator rotor shook the miniature fuzes. 
Tests to determine unbalance were standard 
production line procedure and the methods are 
discussed in Sections 4.6 and 6.4. 

• 

Generators and Power Supply 

In testing generators it was necessary to de- 
termine that the bearings ran smoothly and 
that the rotor would not break at high speeds. 
It was also necessary, of course, to see that the 
developed A and B voltages met specifica- 
tions. 7 - 34 Tests were made with the generator 
working into a mockup of a typical rectifier- 
filter section. 

This mockup rectifier-filter section consisted 
of four half-wave vacuum-tube rectifiers with 
series resistors to match the forward resistance 
of an average rectifier assembly and a parallel 
resistor to match the average leakage resist- 
ance (see Figure 32). 

Tests on completed power supplies were 
made while working into a typical load. Gen- 
erators or power supplies not attached to fuzes 
were driven by air turbines or high-speed 
motors. 

Adjustment of the A and B voltages devel- 
oped by the generator was accomplished by 
overmagnetizing the rotor and demagnetizing 
to the proper amount while the generator was 
under test. Overmagnetization followed by par- 
tial demagnetization was found necessary to 
obtain stable magnets. 12 

Several successful demagnetizing schemes 
were used and one may be found in refer- 
ence 42. 

At this time it would be well to describe 
briefly the types of meters used in measuring A 
voltages. The waveform of the A voltage was not 
quite sinusoidal because of transformer action 


SPECIAL TESTS ON COMPLETED UNITS 


295 


between the A and B windings, which mixed a 
square wave voltage, caused by the rectifier 
load, and a sine wave voltage from the A wind- 
ing which was under a resistive load. It was 
therefore necessary to measure its rms value 
as an indication of its effective, or heating 
power. Ordinary rms meters which used either 
a thermocouple, dynamometer movement, or 
moving vane were unsatisfactory for routine 
tests. The thermocouple meters were sensitive 
to ambient temperature variations, would re- 
spond to stray audio and r-f voltages, were 
very sensitive to overload, and in general were 
of such low impedance that they applied an 
additional indeterminate load on the power 
supply. The dynamometers had very low im- 
pedance, requiring power equal to or greater 


voltage source whose waveform matched that 
of a loaded generator. Calibrated thermocouple 
voltmeters were used as standards. 

Meters whose resistances were 5,000 ohms 
per volt or greater were required to measure 
B and C voltages in order not to load the power 
supply. 

For measuring the speed of rotation of gen- 
erators, tachometers were designed that were 
actuated by the frequency of the A voltage. In 
general, the tachometers consisted of an ampli- 
fier, wave clipper, and vacuum-tube voltmeter 
which read the average voltage across an RC 
net work. A number of circuits were developed 
for this purpose 8 - 22 but the most satisfactory 
one, as well as the one used most extensively, 
is shown in Figure 18. 



Figure 18. Circuit diagram of tachometer used for measurement of rotational speeds. 


than the total generator output. The moving 
vane meters were extremely frequency de- 
pendent and vefy insensitive at frequencies 
greater than 500 c. A vacuum-tube voltmeter 
was developed for laboratory use but was un- 
satisfactory for routine testing. It was demon- 
strated that the waveform between generators 
of a given type were sufficiently uniform to 
allow the use of rectifier-type meters, provided 
these meters were frequently calibrated with a 


7 6 SPECIAL TESTS ON COMPLETED UNITS 

76,1 Introduction 

Although the observations in the final test 
position (referred to in Section 7.4 and de- 
scribed in detail in Section 7.8) provided the 
most important data on completed fuzes, other 
special or supplementary tests were required. 
The nature of these tests varied with the type 


SECRET 


296 


LABORATORY TESTING OF FUZES 


of fuze. Some were 100 per cent or production 
tests, that is, they were performed on all fuzes 
of a particular type. Others were sampling 
tests ; that is, only representative samples from 
production lots were tested. 

The most important of the special tests on 
completed fuzes are described in this section. 


762 Pulse Test 

The pulse test was given each fuze after final 
assembly in its encasing can to insure that it 
was operating electrically after all test leads 
had been disconnected and the encasing can 
staked. The pulse test occurred after the “final” 
test, since the latter was made with a number 
of special test leads soldered to the fuze. An 
r-f pulse of appreciable magnitude was im- 
pressed on the fuze by grounding a metal plate 
near the nose, or grounding the antenna itself. 
If all electric circuits were continuous and 
functioning, the thyratron would fire a simple 
neon firing indicator connected to the detonator 
contacts in place of a detonator. The pulse test 
thus provided a simple overall check of the 
assembled unit in its encasing can. 


7 6 3 Tests of Self-Destruction Circuits 

For those devices with self-destructive [SD] 
circuits (T-5), tests were performed to check 
the length of time required for this circuit to 
function. Both mechanical and electric SD de- 
vices were used. The SD time could be roughly 
measured with a stop watch. However, circuits 
were devised which recorded the time on an 
electric clock. 


Arming Pulse 

An arming pulse test was performed on T-5 
fuzes to insure that transient pulses due to the 
application of voltage to thyratron plate and/or 
disturbances of the r-f field present at the arm- 
ing switch did not fire the thyratron. 5 If the 
thyratron did not fire when armed, the fuze 
was satisfactory in this respect. The test was 


not considered necessary on later models (T-50, 
T-51, etc.), since extensive laboratory tests of 
these designs demonstrated the absence of arm- 
ing pulses. 


765 Warmup 

A warmup test was performed as a sam- 
pling test on T-5 units to insure that initial cir- 
cuit transients were below firing magnitude 
when arming occurred. The transients were 
primarily due to filament warmup and con- 
denser charging. 5 


766 Apex Firing 

An apex firing test was under development 
for mortar fuzes, but such a test was never 
actually performed in pilot production testing. 
The necessary investigations were made, how- 
ever, for the test which was intended to insure 
that the thyratron would not fire at the apex 
of the trajectory where the supply voltages 
developed by the generator dropped to very low 
values. A number of factors occur at the apex 
of the trajectory which tend to fire the thyra- 
tron either as the generator slows down or 
speeds up. 2G 


76 7 RC Arming Delay 

The RC arming delay was measured on fuzes 
which used this type of arming as an additional 
safety feature. The test insured a certain mini- 
mum capacitance for the detonator-firing ca- 
pacitor and an RC product within specified 
limits. Details of these requirements as they 
pertain to RC arming are given in Section 3.3.6. 


768 Shelf Life 

Shelf or storage tests were performed at 
periodic intervals on a group of T-5 fuzes by 
subjecting them to the usual performance 
tests. 31 The most serious effect of long storage 
was detuning (cf. Section 3.1). 


SECRET 


SERVICE TESTS 


297 


" 7 SERVICE TESTS 

7,7,1 Introduction 

The service use of fuzes in wartime involved 
conditions of transportation, handling, storage, 
and installation which imposed severe require- 
ments on design and construction. Ruggedness 
and resistance to extremes of atmospheric con- 
ditions were essential properties of the fuzes if 
they were to withstand rigors of wartime use. 
Some of the extreme conditions involved in 
transportation and storage were mollified by 
the container or package in which the fuze was 
shipped, but the fuze was still subject to con- 
siderable rough handling and atmospheric ex- 
tremes after unpackaging. The bomb fuzes, for 
example, were required to be carried in bomb 
bays for extended periods at very low tempera- 
tures and then to operate properly when re- 
leased. 

The so-called service tests described in this 
section were designed to test the ability of fuzes 
to perform properly under operational condi- 
tions. 


7,7 2 Jolt Test 

Fuzes were subjected to a jolt test (on a 
sampling basis) to test mechanical strength 
and ruggedness of construction. The test was 
performed according to Ordnance Department 
specifications. The jolt machine used for the 
test consisted of a series of arms, operated by 
rotating cams, which held the fuzes (Figure 37, 
Chapter 4) . As the cams rotated, the arms were 
raised in turn and allowed to drop on a wooden 
block. It was required that the fuzes pass criti- 
cal operating tests after jolting. 


Vibration and Packaging Tests 

A vibration test was performed on fuzes to 
simulate conditions resulting from vibration 
of an airplane in flight. The test was adapted 
from the Navy Department Bureau of Ships 
specification for type testing of airborne elec- 
tronic equipment. The test consisted of vibrat- 


ing fuzes at frequencies of from 10 to 55 c at an 
0.06-in. amplitude for 30 min. It was required 
that the fuzes pass critical operating tests after 
vibration. 

Standard ordnance packaging tests were per- 
formed on fuzes in their container. The tests 
included shock, jumbling, and exposure to 
atmospheric extremes. The fuzes were tested 
for overall performance before and after the 
packaging test, and if the fuzes performed 
properly on retest, the packaging was consid- 
ered satisfactory. The packaging tests, except 
for the electric measurements, were made at 
Picatinny Arsenal. 


7,7,4 Temperature Tests 

Two types of temperature tests were made 
on fuzes, one on the completed fuze and the 
other on the head and the power supply. The 
first, a temperature cycling test, was made on 
the completed fuze and simulated the alternate 
extremes of high and low temperature en- 
countered in transportation and storage. The 
fuzes were subjected to a number of cycles of 
high and low temperatures, after which they 
were tested for mechanical and electric per- 
formance. After the test, it was required that 
a fuze meet certain electric and mechanical re- 
quirements which allowed limited changes from 
prior performance. The second test, which was 
performed on the fuze head and the power 
supply separately, was an operational test per- 
formed while the head, or power supply, was 
actually operating under a condition of extreme 
temperature. The temperatures used were —40 
and +60 C. It was required that certain param- 
eters of the head, or power supply, should not 
differ by more than certain small percentages 
from their values when measured at a tempera- 
ture between 20 and 30 C. (See specifications 
listed in the bibliography of Chapter 5.) 


7 7 5 Humidity Tests 

Humidity tests were made in order to dupli- 
cate conditions to which fuzes would be sub- 
jected in tropical climates where during the day 


SECRET \ 


298 


LABORATORY TESTING OF FUZES 


there was high humidity and temperature, with 
lower temperatures and high humidity at night. 
Tests were made in a controlled humidity cham- 
ber where the temperature could be cycled, 
duplicating the breathing as occurs in service 
use. As with the temperature cycling tests, 
performance data after humidity cycling had 
to be within certain specified limits of the prior 
values. (See specifications listed in the bibli- 
ography of Chapter 5.) 


7 ' 7 ' 6 Salt Spray Tests 

Salt spray tests were made to determine the 
effect of the corrosive action of sea water and 
spray. Tests were made according to Army and 
Navy aeronautical specification AN-QQ-S-91, 
with the requirement that the fuzes operate 
satisfactorily both electrically and mechanically 
after treatment. 


7 ’ 7 ’ 7 Centrifuge or Accelerating Tests 

Centrifuging tests were performed to deter- 
mine the effects of appreciable acceleration on 
the fuzes. Only those fuzes which would experi- 
ence accelerations in service were so tested 
(rockets and mortars). The chief defects 
caused by centrifuging were failure of mechan- 
ical parts and displacement of circuit elements 
which created changes in electric performance. 
Both commercial and specially built centrifuges 
were used. The smaller fuzes could be accommo- 
dated in commercial centrifuges, but a special 
double-beam type of centrifuge was built for 
the larger fuzes 4 (see Figures 32 and 33, Chap- 
ter 4) . 


7/7 8 Field Test Set IE-28 

A field test equipment known as the IE-28 
test set was developed for field testing major 
subassemblies of T-5 fuzes. It is shown in Fig- 
ure 19. It was designed primarily to test bat- 
teries before final assembly in the field but was 
also arranged to provide tests for the arming 
switch and the electronic assembly (MC-382). 


The test of the latter was a pulse test similar 
in purpose to the one described in Section 7.6.2. 
Tests on the switch checked the safety (i.e., 
unarmed condition) and continuity of the elec- 
tric detonator. 

Simple laboratory tests of this sort, made in 
the field just prior to use, were considered de- 
sirable for T-5 fuzes primarily because of the 
newness of the fuze as an ordnance item. No 
similar tests were considered necessary or de- 
sirable for generator-powered fuzes. 

The IE-28 test set was made to test either T-5, 
T-6, or T-4 (photoelectric) fuzes. The fuze head 
(MC-380) shown in Figure 19 is part of the T-4 
fuze. b 



Figure 19. Field test set IE-28 with T-4 fuze 
in position for testing. 

7 8 MECHANICAL TESTS AND GAUGING 

781 Introduction 

Mechanical tests were required to insure 
maximum safety of the fuzes and proper opera- 
tion of the mechanical parts, particularly the 
high- and low-speed rotary systems. Gauging 
operations were performed on dimensions 

b This fuze is described in Division 4, Volume 3, 
Summary Technical Report. 


SECRET 


MECHANICAL TESTS AND GAUGING 


299 


which were critical in determining interchange- 
ability of parts or in determining fit or clear- 
ances in Service use. 

7 8 2 Static Torque Tests 

A static torque test was made on the wind- 
mill to determine the torque required to turn 
it from a stationary position. The gauge used 
incorporated a spring device which either indi- 
cated the torque directly on a scale or caused a 
light to glow if the measured torque was 
greater or lower than specified limits. The pur- 
pose of the lower torque limit was to insure the 
existence of sufficient magnetic lock (see Sec- 
tion 3.4.5). Windmills of fuzes meeting this 
requirement would not turn below a certain 
minimum air velocity (about 150 fps). The 
purpose of the upper torque limit was to insure 
that the rotary system was free to turn. 

The static torque test was repeated with the 
fuze under compression 28 and at various tem- 
peratures between —40 and +60 C. This test 
was made to insure free turning of the rotary 
system when subjected to the force produced 
by tightening the booster cup and when oper- 
ated under extreme conditions of temperature. 
The compression applied during the torque test 
was sufficient to give an indication of the com- 
pression strength of the fuze. The force was 
applied (for ring-type fuzes) between the in- 
terrupter plate and the antenna ring. 

A torque test was performed on the detona- 
tor rotor to insure that the force required to 
move this rotor into its final position would not 
be too great on account of possible stiffness in 
the detonator contact springs. The test was per- 
formed with a torque gauge similar to that used 
for the static torque test for the windmills. It 
was found that adherence to the limits of this 
test was an important factor in preventing 
duds. 

78 3 Binding and Dynamic Torque Tests 

A mechanical binding test was performed 
on the completed fuze to insure that no tight 
spots existed in the rotating system due to 
tight or defective parts. If the speed of the fuze 
was within certain limits when driven by a low 


and constant pressure airstream, it was con- 
sidered satisfactory. This same test was per- 
formed under temperatures ranging from —40 
to +60 C to insure that mechanical binding 
would not occur at extreme operating tempera- 
tures. 

A dynamic torque test was made on the 
larger type fuzes, i.e., bomb fuzes, where the 
propellers could be driven by a motor drive. 29 
The purpose of the test was to insure that the 
dynamic torque required to drive the rotating 
system would be within limits which would not 
give undue variations in arming times. Too 
little or too great dynamic torque would cause 
higher or lower propeller speeds respectively, 
with corresponding variations in arming times. 
The torque was measured by means of a tor- 
sion wire, the torque reaction being measured 
by the amount of twist of the wire (Figure 20) . 



Figure 20. Torsion wire dynamometer used to 
measure dynamic torque. 


The torques measured were of the order of 1.3 
in.-oz at 8,000 rpm. 

7 8 4 Other Mechanical Tests 

Dipole strength tests were made on bar-type 


SECRET 


300 


LABORATORY TESTING OF FUZES 


fuzes by applying a force at a point % in. from 
the outer end of the dipole and perpendicular to 
both the axis of the dipole and the axis of the 
fuze. The original test called for an 80-lb 
applied force, while 150-lb force was later 
specified for models which used stronger 
plastic materials in the nose. The requirement 
for the test was that the dipole should suc- 
cessfully withstand several applications of the 
force. 


785 Gauging 

Gauging was performed on dimensions which 
were critical in determining interchangeability 
of parts. Thread gaugings were probably the 
most important operations. In the complete 
fuze assembly three sets of threads were in- 
volved, namely, threads on the casting contain- 
ing the electronic assembly which mated with 
threads in the encasing can (potato masher) ; 
outside threads on the encasing can for screw- 
ing the fuze assembly into the missile; and 
threads on the tetryl cup which mated with 
threads in the encasing can. These threads were 
gauged with appropriate thread gauges. Other 
types of dimensions gauged included diameters 
and depths of holes and overall lengths of parts 
and threads. Ordinary commercial snap, plug, 
sight, and concentricity gauges were used, as 
well as many special gauges developed par- 
ticularly for the jobs at hand. 

In addition to gauging the critical dimen- 
sions mentioned above, measurements were 
made of electric and mechanical arming angles 
and the height of the detonator contact springs. 
These three items were critical because im- 
proper adjustment of any one or all of them 
could cause improper operation of the arming 
system. Electric arming angles were measured 
with an automatic turns counter. Mechanical 
arming angles and contact spring height were 
measured with suitable gauges. 

Vane blade angles of metal windmills were 
measured with a Bausch and Lomb comparator. 
These measurements were important in keep- 
ing the effective pitch of the windmill constant. 
Variation in pitch would, of course, cause vari- 
ations in time to arming (see Section 9.2.2). 


Bakelite windmills were not subject to such 
variation since they were molded. 

The spring tension of the transfer pin con- 
tained in the detonator rotor was measured to 
insure its proper function in springing out to 
release the rotor from the slow-speed shaft and 
then hold it in the armed position. Insufficient 
spring tension might permit the detonator 
rotor to ride beyond the armed position and 
cause a dud, while too much tension would drag 
the shaft with a possible failure of the gear 
train, again causing a dud or excessive drag 
on the generator. It was also necessary to check 
the alignment of the transfer pin with respect 
to the keyway of the slow-speed shaft and the 
arming hole wires; incorrect alignment might 
produce binding of the rotating system. 

Mechanical life tests were not usually run 
except during experimental or pilot production. 
The procedure used in such cases was to sub- 
ject fuzes to mechanical operation for a given 
length of time and then test them electrically 
to determine any changes from previous per- 
formance. This process was then continued in- 
definitely until mechanical or electric break- 
down occurred or until it was apparent that the 
fuzes under test had more than satisfactory 
mechanical life. 


7 9 PILOT PRODUCTION TEST LINE 

791 Introduction 

During the process of unit assembly it was 
desirable to make certain routine checks to in- 
sure the completion of high-quality fuzes and 
a low percentage of rejects. The proper testing 
of units during assembly prevented systematic 
difficulties (lots of poor components or im- 
proper assembly operation) and permitted re- 
pairs while components were accessible. 

Test positions which combined the essential 
laboratory tests and techniques outlined above 
and yet would not appreciably slow down the 
assembly process were, therefore, designed to 
check assemblies at various times during pro- 
duction. 

When designing test equipment for the model 
shops and pilot production lines the most diffi- 


SECRET 


PILOT PRODUCTION TEST LINE 


301 


cult problem was incorporating the special fea- 
tures required by the various types of units so 
that new equipment would not be necessary for 
every fuze model. This requirement led to the 
development of universal test equipment. That 
is to say, equipment was developed in which 
rewiring of the test panels was not required 
every time a new fuze type was to be tested. 
The panel contained switches or plug-in assem- 
blies which could easily be altered as the test 
specifications required. 

In addition, when possible, the equipment 
was “unitized,” that is, made of component 
assemblies which could be used interchangeably 
at different places and could be easily replaced 
in case of failures. For example, the universal 


numerable test jigs were designed and used, 
since the various manufacturers had prefer- 
ences in techniques. Some stressed simplicity, 
some ease of operation, some accuracy, etc., but 
essentially they held the item to be tested and 
were similar to those illustrated below. 

Figure 21 shows a typical test line, which, 
it will be noted, follows the assembly procedure 
outline in Figure 1 of Chapter 6. 

Subsequent Figures 22 to 39, inclusive, show 
pictorial diagrams and schematic circuits illus- 
trating the test positions of Figure 21. The 
illustrations are for one type of fuze ; however, 
modification of the fixtures and voltage dividers 
was all that was required for the other fuze 
types, except for OD and POD fuzes. For the 



Figure 21. Pilot shop production test line. Drawing references are listed in the Bibliography. 


test panel and cathode follower were used in 
five of the ten positions, and the tachometer in 
three positions. 

Since this equipment was to be used continu- 
ously and had to yield data of considerable 
accuracy, prime design factors were simplicity, 
ease of operation, ruggedness, and precision. 
Simplicity and ease of operation could not be 
overstressed, because complexity confused op- 
erators (who were relatively unskilled) and 
made maintenance and calibration difficult. In- 


latter the circuit was arranged to measure plate 
current instead of grid voltage. For the OD 
fuzes an extra switch position was required for 
reading diode voltage. (These models were not 
in production at the close of World War II; 
therefore, the remainder of this section will 
deal with the RGD type fuze. References 2, 5, 
40, and 51 contain details for testing specific 
fuze types.) 

The presentation in the remainder of this 
Section follows the block diagram of Figure 21. 


SECRET 


302 


LABORATORY TESTING OF FUZES 


7 9 2 Oscillator Pretest Position 0 

In the oscillator pretest position, the r-f 
assembly was complete except for the antenna 
ring, cap, or dipoles, since the antenna was not 
added until just prior to the head test position. 
The subassembly was mounted on jigs consist- 
ing of a shield can which contained a properly 
adjusted resistance and reactance load to com- 
pensate for the absence of the antenna. An elec- 
tronic power supply replaced the generator for 
the operating voltages. It might be pointed out 
that any voltage equivalent to 1.4 volts rms was 
satisfactory for the filaments, so that for sim- 
plicity a filament transformer in the power line 
was used. A milliammeter in series with the B 
voltage measured the plate current, while a 
high-resistance voltmeter read the grid voltage 
developed by the oscillator. Any of the vari- 
ous types of wave meters (or receivers) could 
be used to measure the frequency, provided it 
was not too tightly coupled to the oscillator. In 
general, there was sufficient radiation from the 
test leads to operate the wave meter. Otherwise 
a probe was inserted into the shield can. 

For pilot and model shops it was desirable to 
use directly calibrated meters and indicators, 
since the data acquired were used for correla- 
tion purposes. However, production line equip- 
ment was frequently marked so that the 
indicators showed only the tolerance limits. 


Audio Pretest Position* 1 

In the amplifier pretest position, the sub- 
assembly included the amplifier and thyratron 
circuits. Here measurements were made of the 
millivolts to fire, and when necessary, the fre- 
quency shaping and the normal critical voltage 
of the thyratron. The gain-adjusting gimmick 
was set at this test position (in designs which 
incorporated this feature). The millivolts to 
fire were measured at either the amplifier peak 
frequency or at fixed frequencies to determine 
the characteristics of the pass band. 

Supply voltages were obtained from regu- 
lated electronic supplies which were set to de- 

c See Figures 22 and 23 and drawing reference 1. 

d See Figures 24 and 25 and drawing reference 2. 


liver prescribed voltages (1.4 volts at 1,000 c, 
140 volts direct current, 7.5 volts, and 2 volts 
direct current) to the amplifier under test. This 



Figure 22. Oscillator pretest position. 


position contained the necessary thyratron fir- 
ing indicator, cathode* follower, and output in- 
dicator, audio voltage source, and voltage 



Figure 23. Schematic of oscillator pretest posi- 
tion. 


divider. The voltage divider was in the form of 
a plug-in assembly which could easily be 
changed when testing other types of amplifiers. 




PILOT PRODUCTION TEST LINE 


303 


This position consisted of the following unit- 
ized panels: (1) regulated power supply, (2) 
universal test, (3) audio oscillator, and (4) 
the necessary jigs. 

For those fuzes which had the rectifier and 
filter circuits housed in the audio compartment 



Figure 24. Audio pretest position. 

(T-82, T-132, T-171, T-172), power supplies 
were provided to furnish a-c voltage to the rec- 
tifier-filter network. In the latter cases, it was 
possible to make a spot check of millivolts to 
fire with these components in operation. 


794 Audio Prepot and Postpot Test 
Positions 6 

After the oscillator and amplifier were con- 
nected together and assembled into the chassis 
(casting), quick checks of oscillator grid volt- 
age, plate current, millivolts to fire, and normal 
critical voltage were made to insure no errors 
had been made in assembly. Then, after the 
assemblies were potted, they were again 
checked to eliminate those units whose charac- 
teristics had changed abnormally during the 
potting process. Certain small systematic 
changes were expected because of the change 
in stray capacitance caused by the added dielec- 
tric material. 

These test positions were similar to the audio 
e See Figures 26 and 27 and drawing reference 3. 


pretest except for the addition of a grid voltage 
meter and a jig which contained an r-f load 
similar to that used in the oscillator pretest 
position. 

7 9 5 Head Test Position £ 

When a fuze assembly reached the head test 
position, it was completely assembled except 
for the power supply. The antenna cap, ring, or 
dipole (depending on the type of fuze) had 
been sealed in place. Here any final adjustments 
were made, g such as final setting of the gain 
control gimmick and determining the value of 
the padding resistor which normalized the B 
load of the headed unit. Normalizing of the B 
load was essential to keep the C bias within 
specified limits (see Section 3.4.5). 

The test panel was identical to the audio post- 
pot panel except for the jig. 

The r-f jig consisted of a 2-ft shield box con- 
taining the necessary mount and lead connec- 
tions. An r-f load (as described in Section 
7.2.4) matching the free-space load was con- 
sidered part of the r-f jig. Sensitivity and 
stability tests were made at this position as 
required. 


7 9 6 Generator Test Position 11 

The generator was checked not only for the 
A and B voltages developed across specified 
loads, but also for alignment of rotor and pole 
pieces and the ability of the rotor to withstand 
high speeds. With the newer rotors, the latter 
becomes less important. Heavy mechanical 
shielding was necessary, however, to confine 
rotor fragments if one should fracture. 

The A voltage was measured with conven- 
tional a-c voltmeters when the proper resistive 
loads were applied across the windings (see 
Section 7.5.8). The B voltage was rectified and 
filtered with a mockup vacuum-tube rectifier 
which was adjusted to duplicate characteristics 
of an average rectifier-filter section. In general, 

f See Figure 28 and drawing reference 4. 

s It should be mentioned that at this test position, the 
diode resonant circuit of OD units was tuned and locked. 

h See Figures 29 and 30 and drawing reference 5. 


SECRET 


304 


LABORATORY TESTING OF FUZES 




Figure 26. Audio prepot and postpot test posi- 
tion. 



Figure 27. Schematic of audio prepot and post- 
pot test position. 


SECRET 


PILOT PRODUCTION TEST LINE 


305 


the voltages were measured at specified speeds, 
and occasionally regulation data was obtained 
at this test position. Regulation and B/A ratio 
tests were not performed as routine tests and 
usually required precision circuits (see Section 
3 . 4 . 5 ). 



Figure 28. Head test position. 


While at this position, the rotor was de- 
magnetized until the proper voltages were 
obtained or until a slightly higher voltage was 
obtained. The latter procedure permitted 



Figure 29. Generator test position (Bowen). 


further demagnetization at a later test posi- 
tion to compensate for differences in loads and 
rectifier-filter performance. 

Rectifier-Filter Test Position 1 

The rectifier-filter section consisted of a 
* See Figures 31 and 32 and drawing reference 6. 


resistor-condenser network which rectified and 
filtered the a-c B voltage. Taps were included 
for the required C-bias voltage or voltages. In 
addition, this assembly usually contained the 
contacts for the detonator rotor. 

An a-c voltage was supplied to the rectifier- 



Figure 30. Schematic of generator test posi- 
tion. Rla and Rlb — load resistors adjusted as 
specified. X and Y adjusted to match ideal 
rectifier assembly. 

filter section from a generator whose output 
impedance was similar to that of the fuze 
generator. The a-c voltage required to produce 
a given d-c voltage across the output and the 
no-load source voltage were measured. These 



Figure 31. Rectifier filter test position (Bowen). 


two values give an indication of the efficiency 
of the rectifier subassembly. 

Metering circuits for measuring the C bias, 


SECRET 




306 


LABORATORY TESTING OF FUZES 


the a-c ripple across the B load, and the con- air turbine driver, contact prods, and the A 
tinuity of the detonator leads were included. and B loads. 


Power Supply Test Position 3 


Final Test Position 11 


After assembly of the generator and rectifier- 
filter, the completed power supply was tested 



Figure 32. Schematic of rectifier filter test posi- 
tion. Mi — 0-400 volts alternating current, M 2 
— 0.200 volt direct current and 0-10 volt alter- 
nating current. Filter section to see a total load 
(Rl) of 8,000 ohms ± 2 per cent including meter 
resistance. Effective impedance of source looking 
back from points X-X shall be 7,700 ± 1 per 
cent including R and meter resistance. Reactive 
component shall be less than 1,000 ohms. 

and the voltages adjusted for the proper fuze 
load. This final adjustment was accomplished 
either by demagnetizing the rotor or loading 
the B filter and adjusting the C-bias network. 



Figure 33. Power supply test position. 


The test panel contained the necessary A, B, 
and C voltage meters, a tachometer, and de- 
magnetizing equipment. The jig contained an 
j See Figures 33 and 34 and drawing reference 7. 


The performance of a fuze at final test was 
established as the basis for product acceptance. 



tion. 

For this reason, this test position was most 
elaborate. Here the critical electric voltages 
were measured (A, B, and C, oscillator grid 
bias, millivolts to fire, and effective critical 
voltage) under conditions which simulated as 
near as possible free-flight conditions. The free- 



Figure 35. Final test position for ring-type 
fuzes. 

space r-f load was duplicated in a shielded box 
or chamber, as described in detail in Section 
7.2.4. The fuze was mounted on a mechanical 
k See Figures 35, 36, 37, and 38 and drawing reference 

8 . 


SECRET 




PILOT PRODUCTION TEST LINE 


307 


system which permitted vibration, while the 
circuits were operated by power supplied by 
the fuze generator. The generator was driven 
with a stream of high-velocity air directed 
through suitable jets at the vanes of the wind- 
mill. 



Figure 36. Final test position for bar-type 
fuzes (Zenith). 


The most difficult problem connected with the 
final test position was the securing of adequate 
contact to the test points and obtaining the 
proper vibration as discussed in Section 7.4.1. 
With the standard size fuzes, test leads were 
soldered to the connecting lugs on the amplifier 
base plate, as no other system was devised 
which permitted good contact under the neces- 
sary conditions of vibration. (See fuze on table 
in Figure 6.) In designing the miniature fuzes, 
special terminal boards (side view, Figure 14B) 
were incorporated which made possible the use 
of small, quick-acting clamps on which were 
mounted all the necessary test prods. 

The test panel consisted of a tachometer and 
universal panel with the voltage meters, audio 
input and output circuits, and effective critical 
voltage measuring equipment. 

The fixture was a shielded box or metal 
chamber containing the r-f load, air jet, and a 
resonant vibration mount similar to those de- 
scribed in Section 7.4.2. and Figures 2 and 5. 

High-velocity airstreams were the most prac- 
tical method of driving the windmills or tur- 
bines. The air was obtained from a line 


(pressure at 80 to 100 psi) and directed at the 
vanes through jets made from dielectric ma- 
terials. The first jets were made of glass (see 
Figure 39). Plastic jets soon replaced these 
since the mortality of glass jets was very high. 
In places where r-f loading was not important, 
metal jets were used (see Figure 51, Chapter 
4). The jet assembly consisted of an air 
reservoir from which vents issued. These vents 
were directed almost normal to the vane sur- 
face with a slight incline toward the leading 
edge to direct the airflow beyond the propeller. 
Typical plastic jets are shown in Figures 5, 
14B, and 15. Jets of this type consumed approx- 
imately 20 cu ft per min. 



Figure 37. Inside view of final test position for 
bar- type fuzes (Zenith). 


7 9 10 Pulse Test 1 

The pulse test was the last test made on a 
fuze before packaging. The fuze was at this 
point complete except for explosive elements. 


1 See Figure 39 and drawing reference 9. 


SECRET 



308 


LABORATORY TESTING OF FUZES 


All the test leads had been removed, and the 
encasing can staked in place. The purpose of 
the test was simply to insure that during these 
final operations no connections were broken or 
no leads short-circuited which would prevent 
the fuze from operating. Removing the test 



Figure 38. Schematic of final test position. 


leads and staking the cans presented oppor- 
tunity for accidents. 

The complete fuze was mounted in a shielded 
box to eliminate extraneous noises and driven 
with an air blast. A neon lamp in series with a 
protective resistor and by-passed by a con- 
denser and resistor were mounted on a deto- 
nator rotor in place of the detonator to serve 
as a firing indicator. 

An r-f disturbance was produced to fire the 
thyratron by grounding an r-f pickup plate or 
by grounding the fuze antenna. The fuze was 
considered satisfactory if the neon fired only 
when the r-f field was disturbed. 


7 10 QUALITY CONTROL TESTING 

710 1 Object of Quality Control 

Quality control laboratories were set up to 
check and control 54 the quality of all types of 
fuzes which reached the production stage. The 
accuracy of testing equipment at these labora- 


tories was necessarily high. In addition, they 
served as a calibration center for checking 
equipment at the manufacturers. It was the 
express function of the quality control labora- 
tory to indicate the trends of test data, note 
defects of manufacture and failure to meet 
specifications, and immediately to report the 
results to the manufacturer. 

Quality control testing was under control of 
the Services; Division 4’s participation in it 
was primarily of an advisory nature. Develop- 
ment of the test equipment used for quality 
control was, however, done largely in Division 
4’s central laboratories at the National Bureau 
of Standards. The intimate relationship be- 
tween design of the equipment and the operat- 



Figure 39. Pulse test position. 

ing properties of the fuzes made development 
of test equipment an integral part of the fuze 
development program. 

Test equipment used in the quality control 
laboratory was the same as used on similar 
tests on the production line. The production 
line, however, included tests on some parts and 
subassemblies which were not duplicated at 
quality control. 

As mentioned in the introduction to this 
chapter, the sequence of operations at quality 
control was, in general, the reverse of those 
used on the production line. Quality control 


SECRET 


QUALITY CONTROL TESTING 


309 


began with a completed fuze and broke it down ; 
the production line started with parts and sub- 
assemblies which were assembled into a com- 
pleted fuze. Another difference was in the 
nature of the data taken. Actual values were 
recorded at quality control, whereas limit 
meters were usually used in production. 

Eighteen typical fuzes from each lot of 1,000 
were submitted to the quality control labora- 
tory. Later, as quality improved, smaller 
numbers were submitted. These samples were 
selected at random from regular production by 
a representative of the contracting officer sta- 
tioned at the factories. Tubes submitted to 
quality control were selected in a similar 
manner. 

The routing of fuzes in the laboratory is 
shown in the following diagram (Figure 40) 
which is discussed briefly. The discussion will 


mentally or on fuze models which had not 
reached the production stage. 

Quality control tests were of three general 
classes: (1) production, (2) sampling, and (3) 
type. The first were performed on all fuzes in 
the sample (the same tests were also presum- 
ably made previously by the manufacturer). 
Sampling tests were made on only two or three 
fuzes from each sample lot. These tests were 
more difficult to perform and impaired the 
quality of the fuze so that it was no longer 
suitable for field use. Type tests were usually 
of the same general nature as sampling tests, 
but were made only at irregular intervals. Par- 
ticular occasions for making type tests were 

(1) on the qualification lot of a new design, 

(2) when a change in production procedure 
had been made which might conceivably change 
the properties of the fuzes, and (3) when 



Figure 40. Flow diagram for quality control. 


show only the position which each test occupied 
in the quality control program, since a detailed 
discussion of each has been included earlier in 
this chapter. Tests mentioned previously, but 
not included here, were used only experi- 


production tests had indicated an undesirable 
trend in the product. 

In the following discussion the letters P, S, 
and T are used to indicate whether the tests 
were production, sampling, or type. ST indi- 


310 


LABORATORY TESTING OF FUZES 


cates type tests which were often run as 
sampling tests. 

7.10.2 Mechanical Tests and Gauging 

Upon being received and checked in, a lot of 
fuzes was routed to a laboratory where mechan- 
ical and gauging tests were performed. These 
tests included 

1. Gauging of mechanical arming angle (P). 

2. Measurement of propeller turns to electric 
arming (T). 

3. Gauging height of detonator contact 
springs (S). 

4. Gauging of detonator rotor housing (P). 

5. Gauging of detonator rotor and transfer 
pin (P). 

6. Measurement of tension of spring in 
transfer pin; alignment of transfer pin (P). 

7. Gauging of tetryl cup and tetryl plate (P) . 

8. Static torque test (P). 

9. Detonator rotor torque test (S). 

Tests on gear trains were run on a sampling 
basis on the product used by the fuze manu- 
facturer. Gear trains from finished fuzes were 
not tested separately. 

Following mechanical tests and gauging, a 
visual inspection (P) was made for the purpose 
of noting possible mechanical defects, poor 
workmanship, or extraneous materials. 


710 3 Overall Electric Tests 

While the fuze was in the mechanical labora- 
tory, in its encasing cans, it was given the 
pulse test (P). (See Section 7.6.2.) The encas- 
ing cans were then removed from all fuzes in 
the lot and the lot sent to the electric laboratory 
where the test leads were soldered in place. 
There the fuze was given the following electric 
tests and the mechanical binding test (final 
test position, Section 7.9.9). 

1. A, B, and C voltage (P). 

2. Diode voltage for OD fuzes (P). 

3. Oscillator grid bias voltage (P). 

4. Oscillator plate current for POD fuzes (P). 

5. Carrier frequency (P). 

6. Peak audio frequency (P). 


7. Millivolts to fire at one or more frequencies (P). 

8. Effective critical voltage and/or noise margin test 

(P). 

9. Normal critical voltage (P). 

10. Thyratron grid circuit voltage drop (P). 

11. Mechanical binding test (P). 

In connection with certain of the final per- 
formance tests, it should be pointed out that 
data for curves of millivolts to fire versus audio 
frequency, curves of effective critical voltage 
and C volts versus generator speed, and curves 
of A and B voltage versus generator speed may 
be made at the final test position. The milli- 
volts-to-fire curves indicate the frequency 
characteristic of the amplifier, the intersection 
of the effective critical and C voltage curves 
show the lowest speed at which the generator 
can operate without premature firing of the 
thyratron, and the A and B voltage curves in- 
dicate the regulation characteristic of the gen- 
erator. Such data were usually taken on a 
sampling or type basis. 


7 104 Head Tests 

Following the final performance test, part of 
the lot was given the head test which consisted 
of the following. 

1. Tuning for OD fuzes (S). 

2. Oscillator stability test (ST) . 

3. R-f sensitivity test (ST). 

4. Oscillator plate current test (ST). 

All head tests on a group of units were usually 
performed by one operator, though not neces- 
sarily at one test position. An external voltage 
supply was used to furnish power (usually 
alternating current for the filaments and direct 
current for the plate supply). 

710 5 Special Tests 

After the head test, various fuzes of the lot 
were routed to the remaining tests included on 
the diagram, namely, 

1. Destructive mechanical tests. 

a. Dynamic balancing tests (ST). 

b. Strength tests (S). 

c. Vane pitch measurements (S). 

2. Jolt test (ST) . 

3. Vibration test (ST). 


SECRET 


QUALITY CONTROL TESTING 


311 


4. Humidity cycling test (ST) . 

5. Temperature cycling test (ST). 

6. Extreme temperature performance tests (ST). 

7. Salt spray tests (ST). 

The strength tests included dipole strength 
tests (T), for bar-type fuzes, and compression 
tests (ST) on the complete fuze assembly. 


7 10 6 Tube Tests 

Tubes were supplied to the fuze manufac- 
turers by the Army. In order to maintain the 
quality of the tubes as furnished, the Army 
also required that quality control tests be run 


on tube production. The tests performed were 
essentially those outlined in Section 7.5.2. 

7.10.7 Limits and Tolerances 

The limits and tolerances of performance re- 
quired in quality control were somewhat arbi- 
trary. In general, a compromise was made be- 
tween ideal performance and allowances neces- 
sary to maintain production. Figures 8, 9, 18, 
and 19 in Chapter 6 indicate for some param- 
eters the degree of uniformity that was ob- 
tainable. The limits imposed for the various 
fuzes are given in the specifications listed in 
the bibliography of Chapter 5. 


SECRET 


Chapter 8 

FIELD TESTING OF PROXIMITY FUZES’ 


81 GENERAL INTRODUCTION 

T hroughout the development of radio 
proximity fuzes for nonrotating projectiles, 
field tests were relied upon to provide informa- 
tion under conditions which, because of igno- 
rance of what such conditions were or because 
of the difficulties involved, could not be dupli- 
cated in the laboratory. It was demonstrated 
repeatedly that there was no laboratory sub- 
stitute for field testing. From the first field tests 
in the early part of 1941, in which the charac- 
teristics of the reflected signal were investi- 
gated, to the service acceptance tests, field tests 
gave vital data on conditions under which the 
fuzes must operate, the effects of electrical and 
mechanical changes in design, and the quality 
of the final service fuzes. 

Experience gained in the field testing of prox- 
imity fuzes also provided the basis for the nec- 
essary special instructions for handling the 
fuzes in service use. Although the special pre- 
cautions for handling the fuzes (due primarily 
to the fact that missiles became radio antennas) 
were simple and easy to perform, they were 
essential for the best performance of the fuzes. 

For the performance of these tests, proper 
proving ground facilities for releasing bombs 
from planes and for firing rockets and mortar 
shells had to be provided, and technical meth- 
ods, mainly electronic, photographic, and pyro- 
technic, had to be devised or adapted to provide 
the desired information. At first, when the vol- 
ume of field tests was small, the facilities of 
established proving grounds were used, but 
later, as the volume increased, most of the test- 
ing of proximity fuzes was done in new proving 
grounds or ranges set up or reserved for the 
sole purpose of testing proximity fuzes. How- 
ever, special tests continued to be performed in 

n This chapter was prepared by Theodore B. Godfrey 
of the Ordnance Development Division of the National 
Bureau of Standards. David C. Friedman of the same 
organization assisted in the preparation of parts of 
Section 8.2. Section 8.4, including photographs and 
diagrams, was taken almost in its entirety from Chap- 
ter 7 of the Final Report of the University of Iowa. 42 


other locations, particularly tests on effect fields 
and demonstrations performed at the request 
of, or in cooperation with, particular branches 
of the Armed Forces. 

The first field tests in connection with the 
development of bomb fuzes were performed in 
the early part of 1941 at Camp Springs, Mary- 
land, the Naval Air Station, Lakehurst, New 7 
Jersey and the Naval Proving Ground, Dahl- 
gren, Virginia. The greatest part of subsequent 
bomb fuze testing was performed at the Aber- 
deen Proving Ground, although important tests 
were also performed at Dahlgren, Virginia, 
Eglin Field, Florida, and Edgewood Arsenal, 
Maryland. At Aberdeen alone some 14,000 
bombs were dropped in the field testing of bomb 
fuzes. 

In February of 1942, rocket fuze tests were 
started at the Aberdeen Proving Ground. The 
need for additional facilities was soon evident, 
and a new proving ground was established at 
Fort Fisher, North Carolina, where test firing 
started in May 1942. Special tests, particularly 
those in which high-explosive [HE] loaded 
rockets were used, continued to be made at the 
Aberdeen Proving Ground. In the early part 
of 1943, a second proving ground, devoted to 
tests of proximity fuzes alone, was established 
at Blossom Point on the Potomac River, about 
40 miles south of Washington, D. C. At first, 
because of the presence of a commercial air lane 
over this proving ground, firing was restricted 
to low elevations, but later in the year, after 
the air lane had been shifted to the west, per- 
mission to fire at any elevation was obtained. 
In December 1943, the proving ground at Fort 
Fisher, where approximately 11,000 rounds had 
been fired, was abandoned. At the Blossom 
Point Proving Ground nearly 14,000 rocket and 
mortar rounds were fired up to September 1, 
1945. 

The firing of mortar shells in connection with 
the development of the mortar shell proximity 
fuzes was started at Blossom Point in April 
1944 and at the Clinton Field Station near 
Clinton, Iowa, in May 1945. Up until Septem- 



312 


BOMB TESTS 


313 


ber 1, 1945, approximately 1,950 mortar rounds 
were fired at Blossom Point and approximately 
1,700 rounds at Clinton. 

Since the methods used in the developmental 
field testing of bomb, rocket, and mortar shell 
fuzes were often the same or very similar, some 
repetition has resulted in order to make Sec- 
tions 8.2, 8.3, and 8.4 each reasonably complete. 
When more details than are given in one par- 
ticular section on some particular method are 
desired, they will often be found in one of the 
other sections. Details of proving ground tech- 
nique are treated most fully in Section 8.4 on 
mortars; the described methods of testing are 
more numerous in Section 8.3 on rockets but 
there is less detail. 

The test procedures described are, in gen- 
eral, those employed in tests performed under 
direct supervision of Division 4 (at Blossom 
Point, Aberdeen, and Clinton, particularly). 
Safety precautions, except as they were peculiar 
to proximity fuzes, are not discussed. The 
Safety and Security Division of the Ordnance 
Department, through periodic inspections, made 
recommendations which were very helpful in 
reducing the hazards connected with field test 
operations. Precautions for proper installation 
of the fuzes to secure best performance are 
discussed. These precautions were incorporated 
in Service manuals issued by the Ordnance De- 
partment for use with the fuzes. 


8 2 BOMB TESTS 

8,2 1 Introduction 

Field tests of bomb proximity fuzes gen- 
erally involved mounting the fuzes on standard 
bombs and dropping the fuzed bombs from 
standard bombers over the area in which ob- 
servations were made. Both inert and HE- 
loaded bombs were used. 

The great majority of bomb fuze tests under 
the direct supervision of Division 4 were per- 
formed at the Aberdeen Proving Ground. Fig- 
ure 1 as a graphical representation of the accu- 
mulative total number of bombs dropped at 
Aberdeen. 

Experiments with inert bombs were made 


to obtain information on the following points. 

1. Fuze reliability. 

2. Height of function. 

3. Fuze generator characteristics (speed, 
speed regulation, bearing performance). 

4. Arming distance. 

Experiments with HE-loaded bombs were 
made to obtain information on the following 



Figure 1 . Accumulative number of bombs 
dropped at Aberdeen. 


points in addition to those listed for inert 
bombs. 

1. Minimum separation in train required to 
eliminate mutual interference. 

2. Fragmentation pattern. 

3. Optimum height of burst. 

4. Effectiveness of air burst in comparison 
with ground burst. 


822 Bombs Used 

Standard bombs were generally employed in 
field tests and included those listed in Table 1. 
The weights given are nominal. 


314 


FIELD TESTING OF PROXIMITY FUZES 


In addition to these standard bombs, other 
vehicles used have included the T-15 and T-16 
fragmentation bombs, various fighter fuel tanks 


Table 1. Bomb types. 


Type 

Designation 

Weight 

(lb) 

General purpose 

M-30 

100 


M-57 

250 


M-64 

500 


M-65 

1,000 


M-66 

2,000 

Semi-armor-piercing 

M-58 

500 

Light case 

M-56 

4,000 

Fragmentation 

M-88 

220 


M-81 

260 

Incendiary 

M-76 

500 

Chemical 

M-47 

100 


M-70 

115 


M-78 

500 


M-79 

1,000 


modified to carry napalm, and the British 
4,000-lb blast bomb. 


Preparation of Bombs 

The location of the bomb at the time of func- 
tioning of the fuze was obtained by photo- 
graphic methods. Therefore, the preparation of 
HE-loaded bombs for tests of proximity fuzes 
presented no special problems, since the high 
explosive provides its own photographic flash. 
Other than the observance of standard pre- 
cautions in the handling of HE-loaded bombs, 
care had only to be taken to insure that the 
fuze and tail were tightly mounted, since ex- 
cessive mechanical vibration or intermittent 
electric contacts might cause random function 
of the fuze. Secure mounting of the fuze and 
fin to the bomb was recommended as standard 
procedure in the Service use of the fuzes. 

The use of inert bombs, however, is to be pre- 
ferred in developmental testing. The handling 
of bombs and the taking of data can be done 
much more conveniently without the hindrance 
of precautions which must be observed when 
high explosives are used. Therefore, a spotting 
charge arrangement to indicate the location of 
fuze functioning was devised for use with inert 
(mainly sand-loaded) bombs. 

Spotting Charge. For the composition of the 
spotting charge itself, a mixture of 76 per cent 


200-mesh potassium permanganate and 24 per 
cent 200-mesh magnesium (proportions by 
weight) was found to be very satisfactory. This 
mixture was loaded into cardboard cartridges, 
5 in. long and 1 in. in diameter. (The prepara- 
tion of such spotting charges is extremely 
hazardous and should be performed only by 
professional fabricators of pyrotechnical de- 
vices.) The spotting charge was taped to the 
rear end of the fuze, one end of the cartridge 
being in contact with the tetryl-filled booster 
cup. 

It was found that the explosion of the booster 
and spotting charge was not capable of ejecting 
the fuze from the nose of a sand-filled bomb. 
Therefore, a steel pipe, 2 in. in inside diam- 
eter, was used to conduct the flame from the 
spotting charge to the tail of the bomb. An 
empty bomb case was used; the bottom of the 
fuze seat liner was knocked out and the tail 
plate removed. A piece of steel tubing, cut to 
the proper length, was inserted into the bomb 
case from the tail end and its forward end 
slipped into place over the fuze seat liner. The 
tail end of the tubing was plugged and centered 
by means of a special funnel through which the 
bomb was filled with sand. The funnel and tube 
plug were removed and the tail plate installed. 
The tail end of the tube was then centered and 
held in place by a tail fuze adapter from which 
the bottom had been cut out or by a special 
plastic plug. 

It was found that fragmentation bombs, 
which have a low HE to total weight ratio, 
could be used satisfactorily for proximity fuze 
tests without sand loading and, therefore, with- 
out the installation of the steel tubing. The 
only preparation required consisted of knock- 
ing out the bottom of the fuze seat liner and 
removing the tail plug. 

With this arrangement the interval of time 
between explosion of the detonator and the ap- 
pearance of flash at the tail of the bomb is of 
the order of 4 msec. 12 ’ 15 After the appearance of 
the flame a dense green smoke, easily visible to 
the eye, is formed. 

8 21 Assembly of Fuze Components 

Fuzes were received for field test minus all 


BOMB TESTS 


315 


explosive components. The detonator rotors 
were loaded at the National Bureau of Stand- 
ards with the use of M-36 detonators (tempo- 
rary developmental designations, T-3-E1, 
BS-5) . The rotors were checked on a special test 
box for detonator continuity and transfer pin 
operation ; only a small fraction of the minimum 
firing current was used in the detonator test. 
The rotors were inspected for projecting det- 
onator contacts and any other roughness which 
might hinder operation. 

The final assembly was done at Aberdeen 
Proving Ground. First, the rotor was inserted, 
the relative positions of the keyways in the 
shaft and rotor housing furnishing a rough 
check on the setting for minimum safe air 
travel. Next, the tetryl-filled plate was dropped 
in and engaged on the projection which held it 
in proper alignment. Then the tetryl booster 
cup was screwed in hand-tight. If the fuze were 
to be used on an inert bomb, the spotting charge 
in a cylindrical cardboard tube (1 x 5 in.) 
was secured to the cup with a short piece of 
2-in. Scotch Tape. 


8 2 5 Assembly of Fuze to Bomb 

The fuze and puff combination was assem- 
bled to the bomb, either in the bomb bay or 
before loading of the bomb into the bay. The 
fuze was screwed in hand-tight when the 
spring-type washer was used and hand-tight 
plus J /2 turn with a wrench when the lock 
washer was used. 

The arming arrangement was examined to 
make sure that the arming wires would pull 
out properly, that there were no kinks where 
the wires might break under the load, and 
that the arming pins would function properly 
(cf. Figure 20, Chapter 4). 

A wrench was used to tighten the fin lock- 
ing nut, special care being exercised to elimi- 
nate rattle and possible consequent early func- 
tioning of the fuze. 

Delayed arming devices, when used, were 
checked for release and for free spin before 
attaching, and for engagement and setting 
after the bomb and fuze had been mounted in 
the bomb bay. 


826 Range Layout 

Although some testing was done over 
ground with cloth targets for aiming points, 
and some over water with rafts as aiming 
points, so many disadvantages became ap- 
parent that a permanent water-target range 
was laid out at Aberdeen. The diagram used 
in locating impact points on this range is 
shown in Figure 2. The land-water boundary, 
not shown, lay close to the observers’ stations. 

The two permanent targets were built on 
piles. The horizontal surfaces (painted white) 
were planked with 2xl0’s on 20-in. centers 
and were about 10 ft above the water. Pile 
clusters were driven about 15 ft from each 
corner to protect the targets from drifting 
ice. A 25-ft pole was erected on each target to 
aid in estimating function heights. 

The inner target, 1,980 ft from shore, was 
30 ft square and was used for tests with inert 
bombs. The outer target, 2,215 ft beyond the 
other, was 20 ft square and was used for tests 
with HE-loaded bombs. No fragments from 
proper functions were ever observed to fall 
closer than the inner target. Fragments from 
random functions, however, fell 3,000 or 4,000 
ft horizontally from the point of burst. There- 
fore, the bombing course was laid over a 
cleared area. 


82< Communications 

Plane-to-ground communication was accom- 
plished with conventional Signal Corps re- 
ceiving and transmitting equipment. The 
bombardier gave a 5-sec warning of “ready” 
and “fire” at moment of release. This was 
audible at each station through a wired inter- 
communication system. In addition, each sta- 
tion was provided with a portable radio re- 
ceiver, which could be used to hear signals 
directly from the bombing plane. 


8 2 8 Testing Conditions 

Routine tests of fuze quality required the 
determination of function score, function 


f SECRET \ 


316 


FIELD TESTING OF PROXIMITY FUZES 





BOMB TESTS 


317 


height, and fuze operation in flight. Factors 
influencing function score and function height 
include fuze sensitivity, vertical component of 
bomb velocity, angle of approach to target, 
and reflection coefficient of the target. To re- 
duce the number of parameters, bombing was 
usually done at a standard speed (200 mph) 
and from a standard altitude (10,000 ft) over 
a large body of water with an essentially con- 
stant reflection coefficient. From laboratory 
tests and results of field tests under these con- 
ditions, the performance under other condi- 
tions could be computed. 

Some tests were carried out under other 
conditions of plane speed and altitude to 
simulate, as far as fuze operation was con- 
cerned, the conditions of dive bombing. It 
proved very difficult to reproduce release con- 
ditions in dive bombing. Accordingly a system 
of release conditions was worked out for 
horizontal bombing in which the striking 
angles and approach velocities of the bomb 
were the same as for various conditions of 
dive bombing. 27 Still other tests were made 
from higher speeds and at higher altitudes to 
test the units under more severe conditions, 
or to test attachments for the fuzes. 


829 Determination of Function Heights; 

Visual Methods 

Function heights were estimated visually 
by a trained observer to make possible early 
discussion of test results and to supplement 
the photographic data, if incomplete. The ob- 
server was aided by the 25-ft pole mounted on 
the target and checked his estimates regularly 
with the photographic heights. The differences 
between visual estimates and photographic 
heights, obtained by trained observers, were 
remarkably small. 

In addition, a camera obscura was often 
used as a visual means of obtaining function 
heights. Battery commander telescopes at the 
north and south stations and triangulation 
were used to obtain the range, so that the 
apparent height could be converted to actual 
height. 

For engineering purposes, however, data ob- 

SEC 


tained by photographic methods were usually 
required because of their greater accuracy. 


8.2.10 Determination of Function Heights; 

Photographic Methods 

Data for photographic determination of 
function heights were obtained by means of 
16-mm motion-picture cameras, placed at the 
north and south stations (see Figure 2). Koda- 
chrome film was exposed at the nominal rate of 
64 frames per sec and was slightly overexposed 
in order to give the correct density for use on 
Recordak Viewers. Usually, a 2-in. focal 
length lens was used, but 15-mm, 1-in., and 
3%-in. lenses were also available. The 1-in. 
lens was used for photographing trains of 
bombs or in other tests where a larger field of 
view was required. 

Normally, the camera was aimed at the 
target, and pictures of function, target and 
impact were obtained without moving the 
camera. However, on some drops it was neces- 
sary to swing the camera to obtain the picture 
of the impact. In such cases the photographer 
would note the azimuth of the splash with re- 
spect to the target. This was obtained from a 
scale mounted on the tripod head of the 
camera support. Often functions of wild drops 
could be photographed because the noise of 
the bomb could be heard, or the bomb seen, 
soon enough to swing the camera toward the 
point of function. 

Each photographer was provided with a 
stopwatch, which he started when the bomb 
release signal was heard over the intercom- 
munication system. Knowing the time of flight, 
he could start the camera a few seconds before 
impact. 

In order to identify each round the photog- 
rapher took pictures of a data board, on which 
were marked the station, the date, the photog- 
rapher’s name, the lens used, and the round 
number. 

In order to provide an easy means of setting 
the scale on the Recordak Viewers, the photog- 
rapher would take a picture at the beginning 
or end of the day’s work of a scale pole from a 
distance of 500 ft, using the same lens as that 

:et 


318 


FIELD TESTING OF PROXIMITY FUZES 


used for the day’s program. The scale pole was 
painted alternately black and white in foot- 
wide strips. In addition, the first and last feet 
were marked with horizontal boards, which 
projected out from the pole. These bars showed 
up, even when the lighting or exposure was so 
poor that the black and white strips did not 
show with sufficient clarity. 

When the film was received in the computing 
room, it was enlarged to a convenient size on a 
Model 10 Recordak Viewer. The picture of the 
target pole was used to set the scale, which 
usually was 1 ft on the pole equal to 2 mm on 
the screen. 

The target was usually near the center of 
the film and was considered to be exactly there 
for purposes of computation. The error involved 
by the assumption was usually small. The 
horizontal distance from function to target and 
the vertical distance from function to splash 
were measured. If flash and splash were not 
in the same frame, the water-land boundary or 
the horizon were used as reference points. If 
the camera had been swung, the irregularities 
in the skyline were used as reference points in 
going from frame to frame, or the cameraman’s 
notes were used to find the azimuth of the 
function. 

Work was then transferred to a plotting 
board (Figure 2), consisting of a scale drawing 
of the range (1 mm equal to 10 ft) with scales 
running through the target perpendicular to 
the line between the camera and the target 
(one scale for each camera position). Addi- 
tional millimeter scales were pivoted at the 
camera station points for locating the function. 
The horizontal distance measured on the 
Recordak, corrected for change in scale, was 
then transferred to the scale on the board, and 
the pivoted scale was passed through the pro- 
jection on the horizontal plane of the apparent 
point of function. The same would be done for 
another camera station. Where the two scales 
crossed would be the projection of the func- 
tion on the horizontal plane. The distances 
from the two cameras would then be read off 
directly from the pivoted scales. The measured 
vertical distances to the point of function on 
the film were then converted to the true vertical 
distances at the proving ground. This gave two 


values for the function height. In order for the 
determination to be acceptable, agreement be- 
tween these two figures within 5 ft was re- 
quired. The average was reported as the func- 
tion height. 

If the camera had been swung so that taking 
the projected distance would lead to too great 
an error, or when this distance could not be 
obtained because of blurring, the pivoted scale 
was passed through the azimuth obtained, as 
described in previous paragraphs. 

It is estimated that the position of the flash 
may be determined by the method just de- 
scribed within 5 ft of its true position. How- 
ever, the position of the flash of the spotting 
charge may not give the true height of function. 
A later section discusses possible error due to 
time lag of the spotting charge (see Section 
8.2.13). 

When very accurate function heights were 
required, a three-dimensional analysis of the 
film data was made. 9 Two projectors were set 
up to represent the cameras used in taking the 
film. The lenses were in the same ratio as those 
used to take the pictures. The range was laid 
out to scale, and a screen with the target loca- 
tion marked on it was set up at the scale dis- 
tance to the target. The two projectors were 
then started and the pictures run, until the 
first sign of the spotting charge appeared. The 
film was then stopped and the cameras pivoted 
about an axis through the optical center of the 
lens until the images of the target coincided 
with the target location on the screen. The 
screen was then moved forward or backward, 
until the images of the spotting charge burst 
coincided. This located the burst in space. The 
apparent height of the burst was then measured 
and the scale of the setup used to convert this to 
actual function height. The accuracy of this 
method depends upon the scale used, the exact- 
ness of the match in lens ratio, and the ability 
of the operator to superpose the images. This 
method may be used to locate in space any por- 
tion of the trajectory made visible by smoke 
tracer or other means. 

8211 Determination of Function Time 

Function times were determined in several 



BOMB TESTS 


319 


ways, depending upon the accuracy required. 
The usual means was visual determination by 
observers with stopwatches. The release signals 
used also depended upon the accuracy desired. 
The least accurate was a voice signal given by 
the bombardier over the plane-to-ground radio. 
The bombardier gave a 5-sec warning, then the 
release signal, when he dropped the bombs. This 
signal could be heard at the various stations 
by means of the intercommunication system. 
There were two types of automatic signals: a 
photoflash bulb on the plane fired when the 
bomb release was operated ; and/or a squegging 
oscillator either started or stopped at release 
which could be heard via radio and the inter- 
communication system on the ground. 

Function time was also determined from re- 
cordings on film or phonographic disks, of the 
output of a radio receiver tuned to receive the 
r-f carrier of the transmitter in the fuze. The 
starting signal, except when the squegging 
oscillator was used, was a standard 1,000-c 
note started as a warning by the chief observer 
and stopped by him when he saw the photoflash. 
When the bombs were dropped in train, this 
observer also recorded the times of random 
functions by momentary pulses of the 1,000-c 
note at each observed function. The fuze carrier 
was picked up by the receiver and its modula- 
tion detected, passed through a limiter 28 and 
recorded. The end of the modulation, except in 
rare cases, was an indication of the function or 
of the impact. By matching the 1,000-c note to 
a standard in the computing room, it was pos- 
sible to run the record at the same speed as it 
was in the field and to obtain several deter- 
minations by stopwatch of the function time. 
By running the record at half or one-third 
speed, the error in time could be decreased. 
When film records were used, the film was 
driven by a synchronous motor, and a neon light 
recorded a time scale along the edge of the 
record of carrier modulation. When the line 
frequency was known, the time from the end 
of the 1,000-c note to the end of the carrier 
could be determined. When the line frequency 
varied too much, a 50-c oscillator 31 was used to 
operate the neon light. 

Flight time was occasionally obtained by 
photographing a clock and the function on the 


same picture, using a high-speed camera. The 
clock was started at the release signal. 

In most of these methods an error arises be- 
cause of the use of one observer’s reaction time 
to start but not to end the recorded interval. It 
has been estimated that the average error in 
observing function times was about 0.2 sec. 

8 212 Observations of Fuze Carrier 
Characteristics 

Investigation of fuze operation in flight was 
accomplished by picking up the fuze carrier and 
recording the modulation on film or phonograph 
disks, or both. Depending upon the frequency 
of the unit, a Hallicrafter S-27 or S-37, equipped 
with a long wire antenna, was used to receive 
the carrier. The audio output was passed 
through a limiter stage 28 to a Presto K-8 phono- 
graphic recorder or to a Dumont 3-in. oscillo- 
graph with a 16-mm camera attachment 29 or 
both. Speakers were also connected to the re- 
ceiver output, one for the operator and one for 
the chief observer. The starting signal, which 
also provided the time scale signal, consisted of 
a 1,000-c note, which was started as a warning 
signal and stopped as a release signal by the 
chief observer. Round identification and perti- 
nent remarks were placed on the record by 
means of a microphone connected directly to 
the recorder amplifier. The radio operator kept 
a list of film run numbers versus round numbers 
for identification of film traces. 

The strength of the fuze carrier, which gives 
an idea of the overall performance of oscillator 
and power supply, was read from an S meter 
on the receiver. 

The modulation may be divided into three 
types: noise, microphonics, and ripples asso- 
ciated with generator operation. The presence 
of noise usually indicated some mechanical 
trouble, such as binding or chattering gear 
trains or bearings, grinding off of parts of gear 
teeth, loose assembly of parts of the fuze or of 
the bomb, or bits of metal in the generator. 
Some of the troubles could be identified by com- 
parison with records made in the laboratory. 

Microphonics were caused by vibration of the 
elements of the oscillator tube and indicated 


SECRET 


320 


FIELD TESTING OF PROXIMITY FUZES 


need for better mounting of the tube or better 
support of the tube elements. 

Generator ripples gave data on the perform- 
ance of the vane or turbogenerator system. A 
sudden change or an irregular variation in 
ripple frequency usually indicated bearing 
trouble. Some types of harmonic content indi- 
cated rectifier failure. 

Considerable reliable data on generator 
speeds could be obtained from records of modu- 
lation of the fuze carrier. However, when ac- 
curate information on the speed characteristics 
of new driving systems was desired, it was 
customary to build special units each consisting 
only of an oscillator, generator, and driving 
system all in the regular fuze housing. In these 
units the plate supply of the oscillator was ob- 
tained directly from the generator, thus provid- 
ing strong modulation. Such units were called 
radio reporters. 1 The radio reporters gave 
superior data on generator speed because there 
was less confusion as to the frequency of modu- 
lation. In fuzes, modulation of the carrier by 
the generator occurs due to filament modulation, 
at generator frequency, and due to plate produc- 
tion, at twice generator frequency. 

Film records were first used to obtain gen- 
erator speed data, but their use was later con- 
fined to those cases in which greater accuracy 
was necessary. 

The film was placed on a Recordak Viewer to 
enlarge the trace to a size convenient for count- 
ing. Since a synchronous motor was used to 
drive the camera, the distance between sprocket 
holes could be used as a time scale. With these 
cameras, when the line frequency was 60 c, the 
time scale was % 0 sec per space between two 
adjacent sprocket holes. The line frequency dur- 
ing the run could be found by counting the 
number of cycles of the 1,000-c starting signal 
per frame space at various points of the trace. 
The average count was taken to be the value to 
be used for the run. On well-regulated power 
lines this scale was very accurate and con- 
venient to use. When the line frequency was not 
constant enough, a 50-c tuning fork oscillator 
was used to light a neon bulb, which left a 
series of dots along one side of the film. This 
could be used as the time scale. 

The generator speed at a given time was ob- 


tained by counting the modulation frequency 
over a short time interval, centered about the 
time in question. This frequency could then be 
converted to generator revolutions per minute 
as follows : 

If the modulation was caused by filament 
ripple, as was usually the case, speed was deter- 
mined by the formula 

c X 60 
6 t X n* 

where s = generator speeds in revolutions per 
minute, 

c = number of cycles counted in time 
interval, 

t = time interval in seconds, and 
n = number of pairs of poles in gen- 
erator. 

If the modulation frequency were due to 
plate ripple from a rectified power supply, a 
factor of 2 would appear in the denominator, 
since full-wave rectification doubles the gen- 
erator ripple frequency. 

Because of harmonic content in the modula- 
tion, it was often difficult to know whether the 
generator voltage frequency was being counted 
or a multiple or submultiple of that frequency. 
Therefore, for accurate work on film, reporter 
units, in which the modulation was deliberately 
enhanced, were used. 

Because film work was slow and hard on the 
eyes, phonographic methods of determining 
generator speed were developed. It was also 
found that the phonographic method would 
yield data in the case of units which had con- 
siderable noise and microphonic modulation, 
which would ordinarily make film work im- 
possible. 

Two methods were generally used. In the 
first, a good record was essential, as any har- 
monic content tended to cause a frequency lower 
than the true one to be recorded. The record 
was played back, and the output of the player 
was led to a General Radio frequency meter, 
whose output was led through a General Radio 
d-c amplifier to a recording milliammeter. The 
trace was a direct frequency versus time curve. 
Corrections were necessary to make up the 
time differences caused by a difference in line 
frequency between the place where the record 


SECRET 


BOMB TESTS 


321 


was made and where it was played. The 1,000-c 
starting signal was used to calibrate the mil- 
liammeter scale. 

The second and most used method of deter- 
mining generator speed 13 depended upon the 
ability to match a note on a record with that 
from an oscillator, either visually or aurally. 
Because the usual record of carrier modula- 
tion had a fairly rapid change in frequency 
(since the bomb and hence the generator were 
accelerating) , accurate frequency determina- 
tion could not be made from the original 
record. A re-recording was made, therefore, 
through an electronic switch, 30 which allowed 
the output of the recorder amplifier to reach 
the cutting head only at definite intervals, 
usually about 0.8 sec, and only for a very short 
time, usually about 0.2 sec. This recording 
sounded like a record of a series of distinct 
monotones, gradually changing in frequency. 
If the frequencies were very high, the original 
record would be played at half speed, while the 
re-recording was made. The new record was 
then played on a turntable, whose speed could 
be adjusted and played at full or half speed. The 
1,000-c note was used for setting this speed, 
and the matching note was obtained from a 
standard oscillator in the radio building of the 
National Bureau of Standards. 

The output from the record was led to a 
loudspeaker and one pair of plates of an 
oscillator (see Figure 3). The output of an 
audio oscillator (Hewlett-Packard 200B) was 
led to a single crystal earphone and to the other 



input switch panel output 

Figure 3. Block diagram of apparatus for de- 
termining generator frequencies. 


pair of oscilloscope plates. The record was then 
allowed to play until a note was reached of 
which the frequency was to be determined. Here 
a stop kept the tone arm from traveling farther, 


and, because of the spacing of the notes, one 
note only would be played over and over again, 
as the arm hit the stop, jumped back a groove, 
and came to the stop again. The frequency of 
this note was matched by varying the fre- 
quency of the audio oscillator, until the two 
notes sounded the same and no beat notes could 
be heard. A Lissajous figure on an oscilloscope 
was used to improve the accuracy of match. An 
exact match would be indicated by a stationary 
figure, but since the frequency of the note on 
the record was changing, even though it 
sounded like a monotone, the attempt was 
made not to get a motionless figure, but one 
which moved only slightly. 

When the frequency had been determined, the 
record was played through from the beginning. 
The time from the starting signal to the match- 
ing note was obtained by a stopwatch, several 
determinations being made. Since the fre- 
quency could be changed into generator speed 
very easily in a manner similar to that ex- 
plained already, the use of this procedure led 
to the determination of points on a generator 
speed versus time curve. By the use of bomb 
velocity versus time curves, these data could 
be translated into bomb velocity versus gen- 
erator-frequency data, and vane slip factor data 
could be obtained. This method was rapid and 
sufficiently accurate for engineering purposes. 
In the case of noisy or microphonic records, the 
ear could discriminate between the desired and 
the extraneous frequencies where an instru- 
ment could not. 

While the ear could not determine whether 
the frequency was the direct generator voltage 
frequency or some multiple or submultiple, the 
general range of speeds could be obtained 
from film or phonographic records of reporter 
units on which the frequencies could not be 
mistaken. 


8,2,13 Special Tests 

Arming Tests 

Because safety and arming data are of great 
importance to the users of variable-time [VT] 
fuzes, there had to be devised tests from which 
it would be possible to obtain data on the arm- 


SECRET 


322 


FIELD TESTING OF PROXIMITY FUZES 


in g time and arming distance. Since the bal- 
listics of the bombs were known, the problem 
reduced to that of finding accurately the time 
to arm of many units with various arming set- 
tings on various bombs. 

Two ways of indicating arming were used. 
In the first, the unit was modified to func- 
tion on arming, so that ground observation of 
arming time would be sufficient. The ways of 
obtaining function time, mentioned previously, 
then applied to these special tests. 

The second way consisted of using units 
which would function normally but with modi- 
fications, such that the carrier modulation would 
be changed in some way at completion of me- 
chanical arming. Reporter units could also be 
arranged in this way. A reporter unit, in which 
the transfer pin did not spring out of the slow- 
speed shaft and in which the plate circuit was 
shorted when the rotor contacts were in the 
armed position, would indicate arming by an 
interruption of the carrier, which lasted until 
the rotor contacts had turned out from under 
the stationary ones. If the filter condenser were 
not grounded until arming, an otherwise normal 
unit would indicate mechanical arming by a 
sudden cut off in modulation, followed by modu- 
lation at one-half the former frequency. With 
a short RC delay incorporated in the arming 
system, this shock would not trigger the fuze, 
which could then ride through to function on 
the target. 

The use of T-2 arming delay units made this 
problem more complex, since safety considera- 
tions prohibited the use of VT fuzes set to func- 
tion immediately after the operation of a de- 
layed arming device whose arming character- 
istics were unknown. Such devices prevented 
the unit from emitting a carrier, until after 
the arming device had dropped off and the 
warmup period was over. 

Since the fuze had to arm normally, even 
though shortly after the release of the T-2 
device, it was possible from ballistic data, the 
generator speed versus time curve, and the arm- 
ing setting of the fuze to determine the time at 
which the delayed arming device dropped off. 
The fuze was usually set to function on arm- 
ing. 

A special unit could have been used for very 


accurate determination of release of the de- 
layed arming device, if more accuracy had been 
necessary. Such a unit would consist of a 
dummy fuze with an oscillator built into it, so 
arranged that the oscillator would be cut off at 
the release of the delayed arming device. A 
laboratory test would provide the field crew 
with the carrier frequency of the oscillator, so 
that it could be tuned in immediately, allowing 
the delayed arming device to be set for short 
aiming periods. The determination of arming 
time would then be the same as that of function 
time, previously described. 

Train Tests 

In order to test the mutual effects of VT- 
fuzed bombs, several tests were made, in which 
bombs were dropped in trains with various in- 
tervalometer settings. Some of these were made 
with HE-loaded bombs, others with inert-loaded 
bombs. In most of these tests, one or more of 
the fuzes in each train was set to function on 
arming and after the other fuzes had armed. 
In this manner it was made certain that there 
would be at least one early function, and the 
stability of the other fuzes in the train could 
be observed. 

Data on the time of early functions were ob- 
tained in several ways. The chief observer, who 
handled the release switch, would put short 
peeps of the 1,000-c note on the record of car- 
rier modulation by momentarily pressing the 
switch at each function. He also used several 
stopwatches to obtain the times of such func- 
tions. A camera was also mounted in the plane, 
and the frames from the time of the first func- 
tion to those of the other functions were 
counted. The relative function times could be 
obtained from this information as the rate at 
which the film was exposed was known. 

Such film would also show the relative posi- 
tion in the horizontal plane of any functions 
occurring close together. A follow-down camera 
would show these from another angle. 

Proper functions over the water were some- 
times hard to locate, because the smoke or flash 
from one would hide another, and, in the case 
of HE-loaded bombs, the curtain of spray 
thrown would obscure the impact positions. In 
such cases it was often necessary to rely on 


SECRET 


BOMB TESTS 


323 


visual estimates of the range of function heights 
for a closely spaced train. 

Dive Tests 

In order to obtain data on the performance 
of VT fuzes in dive bombing, some tests were 
made in which bombs were released at various 
speeds and at various angles of dive. A camera, 



Figure 4. Accumulative number of rockets fired 
from stationary launchers. 

in which a focal plane shutter was operated by 
hand while a rotating shutter was continuously 
driven by a motor, was used to photograph the 
path of the plane. The variations in plane speed, 
dive angle, and point of release led to the 
abandonment of this method in favor of simu- 
lated dive tests. In these tests a pilot flew a level 
course at such an altitude and speed that the 
approach of the bomb to the target was the 
same as it would have been if the bomb had 
been released under certain dive bombing con- 
ditions. The impact angle of the bomb was ob- 
tained by the three-dimensional analysis method 
already mentioned. The use of a high-speed 
camera, combined with the others, made pos- 
sible the determination of terminal velocities. 27 


Determination of Time Lags 

One of the questions which arose during the 
testing program was whether the spotting 
charge appeared at the same place as where 
the fuze function occurred. Static tests were 
made in which a photoflash bulb of known time 



Figure 5. Accumulative number of rockets 
fired from airplanes. 

characteristics was fired at the same time the 
detonator was fired. The explosion of the spot- 
ting charge was photographed by a high-speed 
camera, and the time between firing and the 
appearance of the flash was obtained. 12 It was 
found that the time taken for the explosion to 
travel down the tube from the fuze to the tail 
of the bomb was of the same order of magni- 
tude, 5 msec, as the time for the bomb to travel 
its own length at the usual release conditions 
and function heights, so that the flash would be 
approximately where the fuze was at function. 
It is not known how the speed of puff travel is 
affected by the bomb velocity. It is also not 
known whether the HE burst would occur 
exactly where the spotting charge burst does. 


secret 


324 


FIELD TESTING OF PROXIMITY FUZES 



Figure 6. Range for high-angle rocket firing 
at Fort Fisher. 


The position of the spotting charge function is 
close enough to the expected position of an HE 
burst to be used for all but a few limited appli- 
cations of the fuze. 


8 3 THE FIELD TESTING OF ROCKET FUZES 

Introduction 

Although radio proximity fuzes for rockets 
were developed largely for air-to-air or air-to- 
ground use, most of the experimental data re- 
quired during development could be, and were, 
obtained by firing fuzed rockets from launchers 
located on the ground or on ground-supported 
towers. As required, these data were supple- 
mented by data obtained from tests, some of 
which were quite extensive and which were per- 
formed at Aberdeen, Dahlgren, Eglin Field, 
and Inyokern, in which rockets were fired from 
airplanes. In both types of firing, a large pro- 



Figure 8. View of east and west ranges, 
Blossom Point. 


portion of the rockets were inert except for a 
spotting charge to indicate functioning of the 
fuze. 

Chronologically, but with considerable over- 
lapping, the largest volume of firing of rockets 
under the direct supervision of Division 4, 



Figure 9. Smaller concrete magazines at 
Blossom Point. 


NDRC, was done first at the Aberdeen Proving 
Ground, then at Fort Fisher, North Carolina, 
and finally at the Blossom Point Proving 
Ground, which was located on the Maryland 
shore of the Potomac River about 40 miles 
south of Washington. In Figure 4 accumulative 



Figure 7. View of Blossom Point, looking west 
from the firing tower. 



Figure 10. Large concrete magazine at Blossom 
Point. 




THE FIELD TESTING OF ROCKET FUZES 


325 


curves of rocket rounds fired from stationary 
launchers at the various proving grounds are 
shown. Similar curves for rounds fired from 
airplanes, not including those fired at Eglin 
Field and Inyokern in tests conducted by the 
Armed Services, are given in Figure 5. 


ward the west and northwest from the top of 
the firing tower at Blossom Point. Figure 7 
shows the main group of buildings and Figure 8 
shows the west range and part of the east 
range. A tow target is suspended between the 
poles of the west range. The poles on the right 



Figure 11. Rocket ranges at Blossom Point. 


Figure 6 is a photograph of the range used 
for high-angle firing of rockets at Fort Fisher. 
The main laboratory building appears at the 
bottom of the picture and the balloon hangar 
at the top. As indicated by dust clouds, a rocket 
had just been fired from a mobile launcher 
when this photograph was taken. The beach 
which appears in the upper left-hand corner is 
on the Atlantic Ocean. 

Figures 7 and 8 are photographs taken to- 


are on the east range, which was used for the 
test firing of photoelectric fuzes. The three con- 
crete magazines at Blossom Point are shown in 
Figures 9 and 10. 

A map of the Blossom Point range is shown 
in Figure 11. The directions of fire often used 
are indicated, together with the locations of 
navigation lights which were often used as 
reference points in night firing. 

Details of instruments used in visual and 


SECRET 


326 


FIELD TESTING OF PROXIMITY FUZES 




Figure 12. Budd 4.5-in. rocket (top), Cenco 3.25-in. rocket (bottom), both with T-5 fuzes. 


photographic observations of rockets in flight, 
and of their limitations, are given in reference 
7. Where possible, duplication of the informa- 
tion given there has been avoided in the present 
chapter on the testing of rocket fuzes. 


Rockets and Launchers 

In the chronological order in which the 
rockets became available, the rockets used in 
fuze testing and some of their characteristics 
are given in Table 2. Some of the rockets were 
fired with a variety of propellent charges, but 
in general the table gives characteristics for 


only those combinations most frequently used 
and is intended to give a general picture of the 
variety of test vehicles available. The availa- 
bility of rockets of rather widely different char- 
acteristics made possible a greater variety of 
test conditions. Special values of acceleration or 
maximum velocity could be provided as needed 
to test fuze components under conditions more 
severe than expected in service. Also airspeeds 
could be obtained when firing from a ground 
launcher equal to those expected in firing from 
airplanes. 

The ballistic characteristics are functions of 
temperature and other conditions. The values 
are representative of firings in summer. 


Table 2. Rocket characteristics. 


Fuzed rocket 


Flight at 45° 
quadrant 



Diameter 

Head 

Unfuzed rocket 

Burning 


Max 


elevation 


motor 

head 

wt 

length 

weight 

distance 

Time 

vel. 

Accel. 

Range 

Time 

Rocket 

(in.) 

(in.) 

(lb) 

(in.) 

(lb) 

(ft) 

(sec) 

(fps) 

(g) 

(ft) 

(sec) 

Cenco 

3.25 

3.25 


32 

20 

40 

.12 

675 

175 

10,000 

30 

M-9, etc. 

4.5 

4.5 


33 

38 

50 

.20 

925 

1£0 

12,500 

33 

AR 

3.25 

3.5 

4 

54 

39 

600 

1.0 

1,500 

50 

18,000 

37 


3.25 

3.5 

15 

56 

50 

500 

1.0 

1,150 

35 

16,000 

34 


3.25 

5.0 

37 

62 

72 

450 

1.0 

825 

25 

13,000 

30 

HVAR 

5.0 

5.0 


66 

123 

800 

1.0 

1,375 

45 

29,000 

44 

T-83 

4.5 

4.5 


72 

93 

250 

0.4 

950 

75 

18,000 

35 


SECRET 


THE FIELD TESTING OF ROCKET FUZES 


327 


As explained in Chapter 1, the development 
of the T-5 rocket fuze for the M-8 rocket was 
carried out concurrently with the development 
of the rocket. This meant that no field testing 
could be done until the rockets were available 
unless some interim method could be devised. 
To this end a simple inexpensive rocket was 
designed and manufactured solely for the pur- 
pose of carrying out experimental tests of the 
fuze. This rocket was designed to give essen- 
tially the same acceleration characteristics as 



Figure 13. Four-rail rocket launcher, Fort 
Fisher. 


the M-8 rocket was expected to have. It had a 
314 -in. body. The first models were built in the 
National Bureau of Standards shop and later 
the Central Scientific Company manufactured 
sufficient quantities for the field tests. It was 
commonly referred to as the Cenco rocket. De- 
tails of the construction are not included here 
but may be obtained from reference 40. Some 
testing was done with British rockets but their 
acceleration characteristics were so different 
from those of the M-8 rockets that their useful- 
ness in testing T-5 fuzes was very limited. A 
Cenco rocket with a T-5 fuze is shown in Fig- 
ure 12. A multigrain propellent charge of sol- 
vent-extruded double-base powder having a 
total weight of about 2.65 lb was normally used 
in this rocket. 

The Cenco rockets were usually fired from 
two-rail or from four-rail launchers which were 
fabricated from iron pipes and other iron pieces 


in the shops of the National Bureau of Stand- 
ards and of the Aberdeen Proving Ground. Fig- 
ure 13 is a photograph of a four-rail launcher 
at Fort Fisher mounted on a truck chassis. 

Two-rail launchers were more simple in con- 
struction, but, since they were merely a pair of 
rails upon which the rocket slid when fired, they 
provided no restraint for the upper half of the 
rocket, which therefore could, and sometimes 
did, lift up from the rails at the forward end 
and leave the launcher at a higher angle of ele- 
vation than that of the launcher. 

Figure 14 is a photograph of the forward end 
of a two-rail launcher, constructed, in this case, 
of two lengths of railroad rails. This launcher 
was constructed at Fort Fisher at a time when 
rocket motor blowups on the launcher were so 
frequent, sometimes every other round, that 
launchers constructed of pipes, which are usu- 
ally destroyed in such a motor failure, were 
impracticable. This railroad rail launcher suf- 
fered many motor failures without suffering 
sufficient damage to prevent its continued use. 

The M-8 rockets became available in quanti- 
ties sufficient for the field testing of fuzes about 
the time that laboratory development of the 



Figure 14. Two-rail launcher and target range, 
Fort Fisher. 


fuze was completed. They were then used for 
testing production models of the fuzes, and the 
Cenco test rocket was accordingly abandoned. 

The M-8 series designation indicated HE 
loading, and these rockets had inert-loaded 
counterparts which bore a series of M-9 desig- 
nations. There was no unanimity in the proper 
designation of such rockets having neither inert 
nor HE loading, and such empty rockets were 


328 


FIELD TESTING OF PROXIMITY FUZES 


variously designated as M-8, M-9, empty M-8, 
empty M-9, etc. There were other variations in 
rockets, such as manufacture, fin design, and 
powder trap design, which had a bearing on 
fuze performance (see Chapters 5 and 9). 

All these Army rockets had folding fins, as 
shown in Figures 12 and 15. Toward the end of 



Figure 15. Army 4.5-in. rocket and pipe 
launcher. Blossom Point. 


World War II, the rockets of this type were 
supplied with attachable fixed fins and were 
then designated as T-74 with no differentiation 
with regard to loading. 

The 4.5-in. rockets with folding fins could be 
fired from ordinary iron pipes of suitable inside 
diameters (the inside diameters of most of the 
launching tubes used lay between 4.6 and 4.7 
in.) such as the one of which the breech end is 
shown in Figure 15. Consequently the construc- 
tion and mounting of launchers of any desired 
length for these rockets was a comparatively 
simple matter. 

At the time when tests of fuzes on Navy air- 
craft rocket [AR] and high-velocity aircraft 
rocket [HVAR] started, standard Navy launch- 
ers, such as the one shown in Figure 16, were 
already available and were very suitable for 
proving ground use. 

Additional details of rocket launchers and 
firing procedures will be found, in the form of 
informal notes, in reference 38. 


Loading and Assembly of 
Fuzes and Rockets 

The assembly of rocket fuzes was very simi- 
lar to that of bomb and mortar fuzes as de- 
scribed in Sections 8.2.4 and 8.4.3 and does not 
need to be given in detail. Further details on 
loading, assembly, and storage procedures are 
given in reference 32. 

Except for the T-5 and T-6 fuzes for which 
very satisfactory black powder spotting charges 
were provided as a standard component by 
Picatinny Arsenal, the spotting charges were 
the same cartridges of a mixture of potassium 
permanganate and magnesium powders as were 
used in bomb and mortar shell fuzes. To mini- 
mize fragmentation of the rocket head, which 
was a hazard when early malfunctions occurred, 
the rocket heads were often provided with four 
1-in. holes to facilitate the emission of flame and 
to reduce the pressure inside the head developed 



Figure 16. HVAR rocket on Navy launcher, 
Blossom Point. 


by the explosion of the tetryl and spotting 
charge. The 3.5-in. AR heads which appear in 
Figure 17 are so drilled. Similar holes may be 
seen in the photograph of the Cenco rocket in 
Figure 12. 

The propellant for many rounds of Cenco and 


THE FIELD TESTING OF ROCKET FUZES 


329 



Figure 17. Groups of fuzed projectiles, Blos- 
som Point. 


Figure 18. Fuzed AR and HVAR rockets; fir- 
ing tower, Blossom Point. 



Army rockets was installed at the proving 
grounds. Since these rockets are obsolete, refer- 
ence is made to the notes given in reference 
32 for details of loading and assembly. The 
Navy rockets were fired as received, except that 
particular care was taken to insure tightness of 
the tail assembly, as described in the notes re- 
ferred to above. Figure 18 shows a group of 
fuzed AR and HVAR rockets at Blossom Point 
ready to be taken to the firing point. 


manner to determine the proportions of proper 
and improper functions. The number of rounds 
fired, when feasible, and the significance of the 
results were determined by standard statistical 
considerations (see Chapter 9). 4>36 ’ 30 The most 
commonly used firing methods were (1) at 
a mock-aircraft target from a stationary 
launcher, (2) high-angle firing tests against 
ground or water targets, and (3) firing from 
an airplane in flight. 


Classification of Field Tests 

The types or classes of information desired 
and obtained from proving ground tests on 
rocket fuzes are listed below. Reference is made 
to the sections in which the methods used to 
obtain particular types of data are described. 

1. Fuze quality (Section 8.3.5) . 

2. Fuze sensitivity and burst surface (Sec- 
tion 8.3.6). 

3. Fuze arming distance (Section 8.3.7) . 

4. Causes of fuze malfunctions and effective- 
ness of remedies (Section 8.3.8). 

5. Exterior ballistics of rockets as affecting 
fuze design and performance (Section 8.3.9). 

Tests of Fuze Quality 
General Procedure 

Tests of fuze quality consisted in firing a 
sufficient number of rounds in some particular 


Target Tests (Horizontal Firing) 

In most target tests efforts were made to 
simulate conditions of air-to-air tactics. The 
rockets were fired almost horizontally at a 
mock-airplane target from a launcher mounted 
on a substantial tower. 

Since the fuzes are sensitive to approach to, 
or departure from, a reflecting surface it was 
necessary to select the firing conditions so that 
ground reflection would not interfere with or 
mask the aircraft target signals. If the fuzes 
were fired horizontally over completely level and 
electrically homogeneous terrain, they would 
receive no firing pulses because there would be 
no relative vertical component of velocity be- 
tween fuze and terrain. While this situation 
cannot be realized physically, it was found pos- 
sible to choose terrain and height and elevation 
of trajectory such that ground reflection signals 
would be negligible. 3 Such signals may arise 
not only from relative velocity between ground 



330 


FIELD TESTING OF PROXIMITY FUZES 


and target but also from sudden variations of 
the reflection coefficient of the surface under 
the trajectory. (Changes in reflection coefficient 


constructed of well-bonded chicken wire with 
wood supports. Figure 19 is a general view of 
the range. Figure 20 is a close-up view of the 
target. Notes on the method of suspending this 
target are given in reference 33. 

A view of the similar range at Blossom Point 
is shown in Figure 8, a diagram of this range 
in Figure 21, and a photograph of the 60-ft 
tower may be seen in Figure 18. The dimensions 


Figure 19. Horizontal target range, Fort 
Fisher. 

would change the load on the oscillator in the 
fuze.) It was found that, with a target mounted 
50 ft or more above ground and a launcher 
about 1,000 ft away and at approximately the 
same elevation, ground reflection signals due 
to relative velocity were negligible. The eleva- 
tion of the launcher was adjusted so that the 
peak of trajectory was between the arming 
point and the target. This arrangement'’ per- 
mitted very rapid firing under conditions which 
were essentially reproducible at any time and 
had other advantages which are discussed in 
Section 8.3.6. 



Figure 20. Mock-plane target, Fort Fisher. 


The first range of this type was set up at 
Fort Fisher. The launcher was about 40 ft above 
ground, the target about 60 ft above ground 
and 1,000 ft from the launcher. The target was 



iJ 

T Target 

S Side camera station 
FT Firing tower 

C Firing point camera, 50 ft above ground and directly 
under projector 

Target poles enclosed an area 100x125 ft 

Figure 21. Diagram of target range at Blossom 
Point. 

of the target, which was usually suspended 70 
to 75 ft above ground, are given in Figure 22. 

As indicated in Figure 21, camera and ob- 
serving stations were located in the towers di- 
rectly below the launcher (with armor plate 
beneath the launcher) and at side stations 
located on lines normal to the trajectory at the 
target. A view of the side observation station 
at Fort Fisher is shown in Figure 23. 

While visual observations were sufficient for 
tests of fuze quality, moving pictures of the 
spotting charge burst were usually taken in 
addition. These supplied the more accurate 
data needed for determining fuze sensitivity 


SECRET - 



THE FIELD TESTING OF ROCKET FUZES 


331 


and burst surface (see Section 8.3.6). Notes on 
observational procedure will be found in 
reference 34. 

High-Angle Firing 

When information on the performance of a 
fuze under more severe conditions was desired, 
the fuzed rockets were fired from the ground 
to function upon approach to water after a long 
flight. Such a test was more severe, since there 
was more opportunity for malfunctions to occur 
caused by generator failure, rocket vibration, 
and fuze microphonics. The angle of elevation 



Figure 22. Diagram of mock-plane target 
(Blossom Point). 


was raised sufficiently so that at arming the 
fuze would be sufficiently far from the ground 
not to be caused to function by the radio waves 
reflected from the earth. Much firing was done 
at elevations of 65 or 70 degrees. 

In high-angle firing, visual and photographic 
observations were made from stations suitably 
located. The locations of stations often used at 
Blossom Point are shown in Figure 11. 



Figure 23. Side observation station, Fort 
Fisher. 


Firing from Airplanes 

While the maximum airspeeds to be expected 
in firing HE-loaded rockets from airplanes 
could be attained in launchings from ground 
locations by the use of lighter rockets, other 
conditions obtaining in actual service use, such 
as the initial airspeed and vibration of an air- 
borne launcher, could not be readily dupli- 
cated. Consequently, from time to time tests 
were made in which fuzed rockets were fired 
from airplanes, usually for function upon ap- 
proach to land or water. Reference 20 gives the 
results of a typical test of this type at Dahlgren. 
Reference 22 gives the results of a test at 
Aberdeen. 


Carrier Indications of Fuze Performance 

As an aid in determining the causes of fuze 
malfunctions, for nearly every round fired the 
presence or absence of fuze carrier was deter- 
mined, and for nearly all rounds of generator- 
powered fuzes, phonograms or cathode-ray 
oscillograms of carrier modulation were ob- 
tained. The circuits used are described in de- 
tail in Section 8.4.3. Figure 24 is a photograph 
of the radio receiving and recording equipment 
used at Blossom Point. 

Carrier modulation records gave evidence of 
microphonics, generator bearing seizure, and 
generator frequency. To determine generator 
frequency the approximate values to be ex- 
pected had to be known, since filament voltage 
ripple produced fundamental modulation fre- 


SECRET 



332 


FIELD TESTING OF PROXIMITY FUZES 


quency and plate voltage ripple twice funda- 
mental, and either might predominate. To 
obtain unambiguous generator speed values, re- 
porter units were used on rockets as discussed 
for bomb tests. Analysis of the records was as 
discussed in Section 8.2.12. 



Figure 24. Radio receiving and recording equip- 
ment, Blossom Point. 


8 ' 3 ' 6 Determination of Fuze Sensitivity 
and Burst Surface 

General Considerations 

In order to correlate laboratory data on the 
electric characteristics of fuzes with expected 
Service characteristics, many tests were per- 
formed to determine the probability and locus 
of function of fuzes passing or approaching 
specified targets at measured speeds and dis- 
tances. Such data were necessary in order to 
assess the effectiveness of a given fuze for a 
given tactical application. An example of such 
an assessment is presented by a series of re- 
ports of the Applied Mathematics Panel (refer- 
ences 19, 20, and 21 of Chapter 1). 

Water-Approach Tests 

One of the simplest methods, and one often 
used, to determine the sensitivity character- 
istics of a given type of fuze is to measure the 
height of function upon approach to water. The 
reflectivity of the target (water) is essentially 
constant at a given location, and the variation 


in sensitivity with aspect can be investigated 
by varying the angle of approach, giving due 
allowance to the varying vertical component of 
the approach velocity. In such tests, assuming 
the ballistics of the fuzed rocket are known 
(cf. Section 8.3.9), the proving ground is 
called upon to provide the photographic records 
from which the height of function over water 
can be determined. 

The determination of height of burst was 
often combined with the obtaining of other 
types of information, such as afterburning 
characteristics (cf. Section 8.3.8) and con- 
sequently was sometimes done in daylight, 
sometimes at night. 

The method of obtaining function heights in 
daylight was the same as that for obtaining 
function, heights of bomb fuzes, except that 
aiming circles were used to obtain triangula- 
tion data. Two or more observation stations on 
surveyed base lines as long as were necessary 
or practicable were used. 

At each station were an aiming circle opera- 
tor and a 16-mm moving picture camera opera- 
tor. Each station was provided with telephone 
or radio communication with all other points 
of operation. 

The distance of the point of function from 
each camera was obtained by use of large plot- 
ting boards. Then since the effective focal 
lengths of the lenses used had been determined 
by photographing scales of known lengths at 
known distances, as described in Section 8.2.9, 
the measured heights of function on the films 
could be translated into actual heights. The 
measured distance on the film was the distance 
between the splash at impact and the first 
visible flash of the spotting charge. Since the 
distance from camera to function was always 
large in comparison to the height of the- camera 
above the water surface, the fact that the splash 
was not directly beneath the point of function 
produced no significant error. 

At night the splash did not appear, and the 
method of determining the height of function 
consequently was somewhat different. Still 
cameras, instead of moving picture cameras, 
were used to photograph the flash of the spot- 
ting charge and lights whose positions and 
heights above water were accurately known. 


SECRE 1 



THE FIELD TESTING OF ROCKET FUZES 


333 


The reference lights were either navigation 
lights or temporary lights placed at intervals 
on a line crossing the area in which impacts 
were expected. 

To reduce the number of films used and de- 
veloped in such tests, special cameras were de- 
signed and constructed. These cameras carried 
8xl0-in. films in holders which could be racked 
down across a horizontal focal plane slit. As 
many as 15 rounds could be photographed on 
one film with such a camera. 

The position of function was determined by 
triangulation on a range plotting board, the 
azimuth of the flash at each station being 
determinable from its position on the film with 
respect to the reference lights. By trigono- 
metrical methods, the apparent height of flash 
with respect to the reference lights could then 
be translated into actual height of function 
above the surface of the water. A value for the 
height of function was obtained for each 
camera and the average agreement in these 
values was of the order of y 20 of 1 per cent of 
the distance from camera to function. 

Target Tests 

While water-approach tests gave data on the 
sensitivity of the fuze with respect to a large 
horizontal reflecting surface, target tests were 
required to determine whether the position of 
the function with respect to an airplane was 
favorable for producing effective damage. When 
sufficient rounds were fired, the positions of 
burst obtained defined a surface, or rather sur- 
faces (because of the radiation lobes of the 
fuze), on which function was most probable as 
a fuze passed the target. 

Before horizontal ranges came into use, such 
tests were performed, mainly at Fort Fisher, 
by firing fuzed rockets at targets supported 
from balloons, using the mobile launcher shown 
in Figure 13. The burst of the spotting charge 
was photographed from two stations, one of 
which was approximately directly beneath the 
target, the other off to the side. A camera was 
also placed near the firing point at times. 
Especially built fixed-focus cameras using 
8xl0-in. plates and equipped with azimuth and 
elevation scales were used in these tests. The 
target was generally an array of crossed dipoles, 


the array being 40 ft long. Figure 25 shows a 
burst on such a target. The balloon used for 
supporting this type of target is shown in Fig- 
ure 26 in its hangar at Fort Fisher. The known 
length of the target was a useful parameter in 
determining the position of function with re- 
spect to the target. 

Because the target position was continually 
changing, and dispersion was large because the 
launcher had to be short to be mobile, these 
tests were time consuming and wasteful of 
ammunition. Many rockets passed the target at 
distances too large to permit the fuze to func- 
tion. With the installation of the ranges for 
horizontal firing described in Section 8.3.4, 
balloon-supported targets were abandoned and 
the testing greatly expedited. Since the target 
was fixed, the launcher had to be only slightly 
adjustable and consequently could be made 
sufficiently long (30 or 40 ft) to reduce ma- 
terially the dispersion of fast-burning rockets. 
Considerable control of the position of the 
trajectory with respect to the target was then 
possible. Moreover, the aspect of the target, 
which was constructed to have approximately 
the reflectivity pattern of an airplane, could 
be readily changed as desired. Still another 
considerable advantage was the fact that the 
camera positions were fixed and could be 
located in such positions (directly beneath the 
launcher and on a line normal to the centerline 
of the range at the target) as to reduce to a 
minimum the operations required to determine 
the position of function. 


8 3 7 Determination of Arming Distance 
or Time 

All proximity fuzes were designed to arm at 
a distance determined by various considerations 
of safety and tactical use. Arming tests in the 
field were performed to determine the reliability 
of arming mechanisms under standard and 
marginal conditions and to obtain data from 
which the statistical distribution of arming 
times, or distances, could be computed. 

The arming arrangement was mechanical or 
electric (RC arming) or a combination of the 
two. With any of these arrangements, the 



334 


FIELD TESTING OF PROXIMITY FUZES 


determination of the time of completion of the 
mechanical arming process was comparatively 
simple and direct. The time to completion of 
RC arming was more difficult to determine. 

Photographic Method 
(Mechanical Arming) 

In the most direct, and most frequently used, 
method for investigations of mechanical arm- 


method could be used only with generator- 
powered fuzes. It involved modifying the fuze 
so that at the completion of mechanical arming 
a recognizable change in the modulation of the 
carrier would occur. The fuze wiring was 
changed so that the detonator rotor contacts 
were in the filter and rectifier circuit. At arm- 
ing, then, a change in amplitude or frequency 
of modulation or both occurred and was re- 



Figure 25. Rocket with smoke tracer and function 
Fort Fisher. 

ing, the fuze was modified to function upon com- 
pletion of mechanical arming, mounted on a 
rocket and fired in the usual manner. The time 
at which the fuze functioned was then measured 
by stopwatch, or the time and locus of func- 
tion were determined photographically. Refer- 
ence 14 includes a description in detail of a 
method for obtaining indications of a number 
of arming functions on one film or plate and for 
interpreting the results. 

Carrier Indication of Mechanical Arming 

A radio method of measuring the time to 
completion of mechanical arming was used 
where feasible, since it had the advantage of 
not destroying the fuze at arming and so allow- 
ing the determination of arming time to be 
combined with other types of testing. This 


on array of crossed dipoles suspended from balloon, 

corded on an oscillograph or sound-recording 
equipment connected to the output of a radio 
receiver. The time of launching was obtained 
on the same record by mounting a switch in a 
1,000-c circuit on the launcher in such a posi- 
tion as to be opened or closed by a fin or other 
part of the rocket as the rocket started to move 
forward. 

Since the time to arming was often too short 
to allow the carrier to be tuned in with a re- 
ceiver of normal selectivity, broad-band re- 
ceivers (made by Zenith) were often used. 
These receivers have a flat frequency response 
over a range of ±3 me. Their main drawback 
is the absence of an r-f stage with consequent 
possibility of direct interference through the 
i-f stages. In addition, they are inherently less 
sensitive than receivers of greater selectivity 


SECRET 


THE FIELD TESTING OF ROCKET FUZES 


335 


and consequently could not always be used 
when desired. 

RC Arming Measurements 

A possible method of determining the time or 
distance to completion of RC arming is to vary 
the distance between launcher and target and 
obtain the distribution of duds and proper func- 
tions as a function of this distance. Some ex- 
periments of this type were performed by firing 
from airplanes to ground as described in this 
section. Otherwise there was no satisfactory 



Figure 26. Balloon in hangar, Fort Fisher. 


method of varying the distance between the 
launcher and a physical target. Instead, in hori- 
zontal firing, a portable sweep-frequency trans- 
mitter was used to supply a triggering pulse to 
fuzes in flight at various positions along the 
trajectory. 

Because of rocket dispersion, the power of 
the transmitter had to be greater than would 
have been necessary if the distance of passage 
had been constant. Consequently, if the trans- 
mitter had been left in continuous operation, 
the position at which the fuze first received a 
signal of firing intensity would have been in- 
definite and could have been up to 200 ft short 
of the point of passage above the transmitter. 
For this reason, a time switch, consisting of a 
thyratron and associated RC circuit initiated 
by a rocket-operated switch on the launcher, 
was used to key the transmitter at the time 
when the rocket was directly over the trans- 
mitter. The interval of time between launching 


and operation of the transmitter was measured 
automatically by means of a time clock. 

It was not possible to apply continuous 
signals or a series of signals because if a pulse 
of sufficient magnitude to fire the thyratron 
were received by the fuze before arming was 
complete, the detonator-firing capacitor would 
“dump” the charge and the arming cycle would 
start over (see Section 3.3.6). Thus the pulsing 
method of measuring arming times gave only 
a “yes” or “no” indication on each round fired. 
Large numbers of rounds had to be fired to 
obtain reliable arming time data. 

This arrangement was used in arming tests 
of the T-30 fuze on HVAR and AR rockets. Be- 
cause of the cessation of hostilities these tests 
were not so extensive as originally planned. A 
progress report on the results is given in the 
Bibliography. 38 

Function, No-Function Tests at 
Various Slant Ranges 

In order to test arming characteristics under 
Service conditions, fuzed rockets, inert or HE- 
loaded, were fired from planes at various slant 
ranges. By determining the ranges of firing 
photographically, the dividing line between 
duds and proper functions could be bracketed 
and the arming distance determined to a degree 
of certainty dependent upon the number of 
rounds fired. This method was applicable to 
the testing of fuzes of any type with any type 
of arming. 


8 ' 3 ' 8 External Causes of Fuze Malfunctions 
Introduction 

Throughout the development of proximity 
fuzes for rockets, much field testing was di- 
rected toward investigating causes, external to 
the fuze, of malfunctions and the effectiveness 
of remedial measures devised to minimize such 
effects. Propellant afterburning and instability 
of rocket parts were particularly troublesome. 
Other factors studied were the effect of temper- 
ature upon setback, upon which arming de- 
pended, the effect of raindrops upon fuze per- 
formance, and the effect of rocket spin upon 
the arming of the T-5 and T-6 fuzes. 



336 


FIELD TESTING OF PROXIMITY FUZES 


Investigations of Afterburning 

Afterburning may be defined as the delayed 
burning of remnants of propellant or other 
combustible material which, for one reason or 
another, remain in the combustion chamber 
after main burning has ceased. (See Section 
9.2.2.) The ionization produced by afterburning 
may cause malfunctioning of the fuze. (See 
Section 2.13.) Numerous field tests were de- 
voted to studying the effect with many fuze- 
rocket-propellant combinations. 24 ’ 38 

Much of the firing in these investigations was 
done at high angles and at night, in order that 
visual or photographic observations of after- 
burning might be correlated with observations 
of the locations of fuze functions. 

A considerable accumulation of data was 
usually required before the incidence of mal- 
functions caused by afterburning could be 
differentiated from the incidence of malfunc- 
tions resulting from other causes. If afterburn- 
ing was observed to occur only in the first part 
of the trajectory, the observed distribution of 
malfunctions in the rest of the trajectory could 
be extrapolated back into the afterburning 
region and the number of malfunctions due to 
other causes in this region subtracted from the 
total in this region to give a residue, the major 
portion of the total in such a case, attributed 
to afterburning. In other cases the analysis 
and interpretation were less straightforward 
and consequently less satisfactory. 

As was to be expected from the frequency 
selectivity characteristics of the fuzes, intense 
afterburning was not necessarily accompanied 
by a high incidence of malfunctions. This was 
supported by static tests in which the pulses 
produced in the output circuit of the fuze by 
afterburning were recorded as cathode-ray 
oscillograms and correlated with simultaneously 
obtained moving pictures of the actual phe- 
nomena occurring and with performance in the 
field. 18 In general, it was found that a triggering 
flame was always a visible flame, but that all 
flames did not necessarily give rise to transients 
capable of triggering the fuze. 

Figure 27, a typical set of photographs from 
night-firing tests, illustrates the great varia- 
tions in afterburning phenomena encountered. 


The M-9 rockets were used in these rounds. The 
appearance of main burning also differs 
markedly with different propellants, as illus- 
trated in Figure 28. 

Effects of Rocket Structure 

At one time or another almost every possible 
source of mechanical or electric instability in 
rockets was suspected and investigated as a 
cause of fuze malfunctioning. The method of 
investigation was the obvious one of statistically 
analyzing the incidence of malfunctions before 
and after making a modification in the rocket 
designed to eliminate the suspected source of 
triggering pulses. As examples, studies were 
made of the effect of electrically bonding the 
joint between head and motor, of the effect of 
electrically bonding the joint between folding 
fins and motor (leaving the fins still movable), 
of the effect of welding the fins rigidly in the 
open position, of the effect of making the trap 
structure more rigid, and of the effect of rocket 
spin (see Chapter 9 and reference 21) upon fuze 
performance. 

The studies of fin structure led to a recogni- 
tion of the necessity of inspecting the locking 
action of folding fins and to the design of a 
crimping tool which was used to make the lock- 
ing action of individual fins more positive where 
necessary. This tool became a standard serv- 
ice item and was provided for use in combat 
areas. 

Effect of Propellant Temperature 
upon Arming 

Since the arming of rocket fuzes depends 
upon acceleration, and acceleration is affected 
by propellant temperature, tests were made to 
determine whether the arming mechanism 
would operate properly at the extreme service 
temperatures of the rockets. The fuzes were 
either arranged to function on arming or the 
incidence of duds with normal fuzes at the ex- 
treme temperatures was investigated. In these 
tests the rocket motors were first brought to 
the desired temperature in thermostatically 
controlled chambers. They were removed and 
fired quickly before the powder temperature 
changed appreciably. A typical test of this type 
is described in reference 16. 


SECRET 


THE FIELD TESTING OF ROCKET FUZES 


337 


Effect of Raindrops upon 
Fuze Performance 

Tests on the performance of fuzes, with and 
without plastic shields, in rain and in clear 
weather revealed that impact with raindrops 


drop size and concentration at the time of firing, 
a method of obtaining permanent records of 
these quantities was developed. 26 Outing flannel 
was impregnated with a mixture containing 
methyl violet. When a square of this material 



REGULAR POWDER 
LEAST AFTER - BURNING 
EARLY AT 2.1 SEC 
(L-I7S3) 


REGULAR POWDER 
AVERAGE AFTER - BURNING 
EARLY AT 2-4 SEC 
(L- 1729) 


REGULAR POWDER 
MOST AFTER - BURNING 
EARLY AT 1.0 SEC 
(L- 1735) 


DRY POWDER 
AVERAGE AFTER- BURNING 
EARLY AT 3.4 SEC 
(L- 1755) 


PUFF AND AFTER -BURNING 
PICTURES , TAKEN WITH 
CAMERA PLACED ABOUT 30 
FEET TO SIDE OF PRO- 
JECTOR AND POINTED TO 
COVER FIRST FEW SECONDS 
OF FLIGHT. INITIAL BLAST 
PARTIALLY OR COMPLETELY 
EXCLUDED 



WET POWDER 
AVERAGE AFTER -BURNING 
EARLY AT 1.4 SEC 
(L- 1736) 



A-41 POWDER A-41 POWDER 

NO EARLY FUNCTION EARLY AT 2.2 SEC 

(L- 1757) (L- 1764) 


PURGE PELLETS 
NO EARLY FUNCTION 
CL- 174 4) 


Figure 27. Afterburning with various propellants, M-9 rocket, Fort Fisher. 


could cause malfunctions the incidence of which 
could be reduced by the installation of plastic 
caps. 

In order to obtain quantitative data on rain- 


was exposed to rain for a measured length of 
time, a purple spot was formed for each drop 
striking the cloth. The diameter of the spot 
was found to be about 85 per cent of the diam- 






338 


FIELD TESTING OF PROXIMITY FUZES 



scale: i i i i — 

O 10 30 



RD B 11131 


_! ! I 

50 75 100 FEET 


RD B 11137 



MJX PROPELLANT 


Figure 28. Main burning with two propellants, T-83 rocket, Blossom Point. 




THE FIELD TESTING OF ROCKET FUZES 


339 


eter of the drop. From such a record, the 
number of drops striking unit area in unit time 
and the diameters of the drops could be deter- 
mined. 

Sympathetic Functioning in Rapid Firing 

Tests of fuzed HE-loaded rockets, launched 
in quick succession, were made to determine 
whether the fuzes would function sympa- 
thetically, that is, whether the ionization or 
fragments produced by a burst would cause the 
fuzes on adjacent or succeeding rockets to func- 
tion also. One fuze in each group of rockets 
fired in rapid succession was modified to func- 
tion at a predetermined time. A rotary, multiple- 
contact firing switch driven by a spring motor 
was provided to fire the rockets with a desired 
interval of time, about y 10 sec, between suc- 
cessive rockets. Moving pictures and visual 
observations were made to determine the time 
and location of bursts. 11 

839 Investigations of the Exterior 
Ballistics of Rockets 

Introduction 

Since the weights and ogives of the rockets 
as used were seldom standard, the ballistic data 
required in the course of the development of 
rocket fuzes were usually obtained at the prov- 
ing grounds, often simultaneously with tests of 
fuze performance. Quantities measured were 
velocity, acceleration, range, angle of terminal 
approach, rate of spin, and yaw. 

The instruments used in these measurements 
included standard 16-mm moving picture 
cameras, a Western Electric 16-mm high-speed 
camera, Hickman 8-mm high-speed cameras, 
ribbon-frame cameras, still cameras with 
rotating shutters, ballistic coils, and a photo- 
electric-radio yaw telemeter. The characteristics 
of the photographic instruments are given in 
Chapter 13 of reference 13. Chapter 4 of the 
same publication describes the mathematical 
procedures used in trajectory calculations (see 
also Section 8.4.4) . 19 - 35 > 45 > 46 

Velocity, Acceleration, and Range 

Velocities were determined photographically 
if values of velocity in a relatively short portion 


of the trajectory (several hundred feet or less) 
were desired; the data were obtained in day- 
light, using high-speed cameras or ribbon- 
frame cameras or both. If velocities throughout 
several thousand feet of trajectory were de- 
sired, the rockets were equipped with flame 
tracers and fired at night. Still 8xl0-in. cameras 
with slotted disk shutters driven by synchro- 
nous motors were used to obtain the position of 
the rockets at known intervals of time. Refer- 
ence lights were used to establish a scale of 
distance from the launcher. 

None of these methods was capable of giv- 
ing velocity curves from which reliable accelera- 
tion curves could be obtained but did suffice to 
give average values of acceleration. Atmos- 
pheric refraction at night was a particularly 
troublesome source of error. 

In horizontal firing from a tower, a timing 
disk driven by a synchronous motor and a small 
mirror through which the launcher could be 
photographed were placed in the field of the 
moving picture camera at the side station. From 
the films so obtained, the average velocity from 
launcher to target and the velocity at the time 
of passing the target could be determined 
whenever desired. 

When the ribbon-frame cameras were new, it 
was found that the synchronous motor drive 
could be depended upon to give exposures at 
twice line frequency at voltages greater than 
90 v, but after repeated use it was found that 
the motor drive could no longer be depended 
upon. The cameras were then equipped with 
neon-bulb timing devices in which the light 
from the bulb, which flashes at twice line fre- 
quency, was led directly to one edge of the film 
through a Lucite rod tapered to produce a 
narrow trace upon the film. At the same time 
it was determined that velocities obtained 
photographically and by means of ballistic coils 
and a cathode-ray chronograph arrangement 
were in agreement. 25 

Range determinations were made by triangu- 
lation from two or more observing stations as 
described in Section 8.3.6. 

Angle of Approach 

More reliance was placed upon angles of ap- 
proach obtained from trajectory calculations 




340 


FIELD TESTING OF PROXIMITY FUZES 


based upon determinations of maximum veloc- 
ities and ranges at various angles of elevation 
than upon angles obtained by photographic 
means. Attempts were made to obtain the angle 
of approach directly by equipping rockets with 
tracers and using cameras placed approxi- 
mately on a line normal to the line of fire at 
the point of impact, but it was found that 
atmospheric refraction over water at night 
introduced errors of such a magnitude that the 
results could not be trusted. 

Determination of Rate of Spin 

Since the rockets used were fin stabilized, 
spin, when it occurred, was usually accidental 
and had a speed of not more than several 
hundred revolutions per minute. Consequently 
the rate of spin was easily measurable. The 
rockets used for this purpose were painted half 
white and half black and photographed in flight 
with a ribbon-frame camera located off to the 
side. 17 

By this technique it was found that accidental 
tilting or bending of the fins of M-9 rockets 
would produce spin of the rocket. This spin 
caused malfunction of the arming switch of T-5 
and T-6 fuzes (see Section 9.2. 2). 21 

Measurement of Yaw 

A few measurements of yaw were made. The 
frequency of yaw of rockets equipped with 
smoke tracers and fired from a plane was deter- 
mined from ordinary 16-mm moving picture 
film. 8 * For one round the frequency and ampli- 
tude of yaw were measured during flight by 
means of a photoelectric-radio telemeter, using 
the sun as a localized source of light. 10 


8 4 THE FIELD TESTING OF MORTAR 
SHELL FUZES 

Introduction 

All mortar shell fuze testing under the 
auspices of Division 4, NDRC, was performed 
at Blossom Point (see Section 8.3.1) and at 
the Clinton Field Station of the University of 
Iowa. Figure 29 is a graph showing accumula- 


tive totals of rounds fired at the two proving 
grounds. 



Figure 29. Accumulative number of mortar 
shells fired. 

The Clinton Field Station was located along 
the Mississippi River about 2 miles north of 
Clinton, Iowa. Figure 30 is a map of the prov- 
ing ground and Figure 31 a photograph of some 
of the buildings in the central area. Figure 32 
is a photograph of the view down range from 
Tower No. 1 and Figure 33 is a view of Tower 
No. 3, which included a fragment-proof shelter. 

The testing procedures used at Blossom Point 
and at Clinton were very similar. The Clinton 
Field Station was designed exclusively for the 
purpose of testing mortar shell fuzes. Conse- 
quently, the practices obtaining at that proving 
ground have been considered particularly 
pertinent in preparing this section of Chapter 8. 

One essential difference between the testing 
of mortar fuzes and other proximity fuzes was 
in the provisions for taking ballistic data. 
Range and velocity measurements were taken 
on most rounds of mortar tests in order to 
provide data on the effect of the fuze on the 
flight of the missile. 


SECRET 


THE FIELD TESTING OF MORTAR SHELL FUZES 


341 



0 

Point on line 

7 

-0- 

Telephone pole 

8 

-©■ 

Power pole 

9 


Base line target 

10 


Fence 

11 

1 

Gun station 

12 

2 

Storage 

13 

3 

Loading shack 

14 

4 

Radio shack and tower 

15 

5 

Office 

16 

6 

Machine shop 

17 


Equipment room 
Head 

Temporary storage 
High explosive storage 
Guard quarters 
Guard house at front gate 
Detonator storage 

KMNO4 and magnesium puff storage 
Board walk from gun station to No. 10 
Added power lines 
Added fence 


Figure 30. Map of Clinton Proving Ground. 




342 


FIELD TESTING OF PROXIMITY FUZES 


8 . 4.2 Personnel and Equipment 

Figure 34 shows the distribution of personnel 
and equipment for a typical test of fuze quality. 
In addition to the 14 men for whom duties are 
listed in Figure 34, three were used in loading 
operations and one for carrying ammunition. 



Figure 31. View of Clinton Field Station. 


The work of developing and reading films, com- 
puting and analyzing data, writing reports and 
handling business details was done in an office 
building in Clinton, 3 miles from the field sta- 
tion. The personnel in this office included four 



Figure 32. View of towers and gun position at 
Clinton Field Station from T± tower. 


persons to assemble data and perform calcula- 
tions, one operator for the film developer, two 
film readers, two secretaries and two men to 
analyze data and write reports. A report could 


be completed in 4 hours after the raw data 
were received from the field. 


8-4 3 Operating Procedures 

Coordination of Firing 

It was necessary to set up a definite routine 
and to exert considerable effort in coordination 
of the firing operation in order to carry out 
smoothly a firing program of 100 or more 
rounds per day. All men were familiarized with 
the test program before going to their stations 
and were kept supplied with pertinent informa- 



Figure 33. View of Ts tower at Clinton Field 
Station. 


tion during the firing program. The firing oper- 
ation began with the gunner placing the shell 
in the release mechanism and asking for clear- 
ance from the tower. The operator in charge 
at Ti ascertained clearance and each of the sta- 
tions informed the gunner of readiness. On the 
informative count of ten, the gunner caused 
the release mechanism to drop the shell down 
the mortar barrel. 

Knowing the approximate time of flight of 
the rounds, it was a simple matter for the 



THE FIELD TESTING OF MORTAR SHELL FUZES 


343 


operator in charge to inform everyone when 
the unit was expected to function. At approxi- 
mately 2 sec before this time, he gave the signal 
“camera.” The cameras were started on this 
signal and the aiming circle operators became 
alert. Much film and time required for reload- 
ing the cameras were saved in this manner. If 
anyone observed an early function or a dud, he 
immediately informed all operators over the 
telephone. These methods relieved the opera- 


sistors shown were separate resistors in order 
to guard against excessive current in case of a 
short circuit of one of them. Figures 38 and 39 
show the fixture into which the rotor was in- 
serted and the testing meter constructed at the 
field. Identical testing devices were used for the 
T-132 and T-172 fuzes except that the contacts 
on the fixtures holding the rotors were different 
because of the designs of the two rotors. Plac- 
ing the interrupter plate (also called the lead 


Bluff 


Personnel for Each of the Towers 

h‘ 14 ** 

1. Camera Operator 

2. * Aiming Cirole Operator 

3. * Telephone Operator, who may 

also operate a second aiming 
circle* 

Gun Position Personnel 

1. Gun Operator — handles telephone 

2. * Operator of Muzzle Velocity Machine 

and B. C. Telescope 


Personnel at Ti Tower 

1. * Operator in Charge — handles telephone 

2. Camera Operator 

3. * Aiming Circle Operator 

Personnel for Radio Building 

1. Operator for Recordings 

2. * Telephone Operator 

3. Camera Operator to photograph oscilloscope 


* These men also handled a stop watoh* 



** T 2 and*T 4 did not operate simultaneously. 


Equipment at Each of the Towers 

12 * 3 * 14 

1. Camera 

2. Two Aiming Circles 
3* Two Stop Watches 

4. Telephone 

5. Blackboard 

Gun Position Equipment 

1* Mortar with Associate Release Mechanism 

2. Muzzle Velocity Measuring Ueohaniem 

3. Stop Watoh 

4. B. C. Telescope 

5. Telephone 

6. Blackboard and Clock to be photographed 
from Tl 


Equipment at Tl Tower 

1. Camera 
2* Aiming Circle 

3. Two Stop Watches 

4. Telephone 

5. Speaker connected to Radio Receiver" 
Equipment for Radio Building 

1. Broadband Receiver 

2. Oscillator 

3. Mixer 

4. Limiter 

5. Recorder 

6. Motor Driven Camera 

7. Oscilloscope 

8. Stop Watoh 

9. Telephone 

10. Headphones 

11. Microphones 


Figure 34. Personnel and equipment at observation towers, gun position, and radio building during 
firing operations. 


tors of undue tenseness and allowed them to be 
alert at the proper time. 

Loading Operations 

The loading operation involved the assem- 
bling of the components (Figure 35) into the 
complete 81-mm shell with the VT fuze as 
shown in Figure 36. A supply of the component 
parts, except the VT fuze, was kept at the field 
station in order ter allow much of the loading 
operation to be carried out before the day of a 
firing program. The loading of the detonator 
into the rotor was the first operation. Figure 
37 is a circuit diagram of the device used for 
testing the rotor after it was loaded. The re- 


or tetryl plate) in the fuze and screwing in the 
booster cup completed the loading of the VT 
fuze. 

Shells as received contained a filler of bismuth 
carbonate in paraffin wax. To facilitate observa- 
tion and photography of the height of func- 
tion, a cartridge containing a mixture of 
potassium permanganate and magnesium metal 
was used to provide a flash and smoke puff. A 
cavity drilled in the shell filler provided a space 
for this cartridge. The hole for the cartridge 
was drilled with a 1-in. bit and reamed to a 
diameter of 1% in. As the program closed, the 
problem of drilling the filler of stearic acid and 
plaster paris presented itself. Because this 


SECRET 


344 


FIELD TESTING OF PROXIMITY FUZES 


filler is so much harder than paraffin, it ap- 
peared that drilling into it would require the 
use of a power-operated setup built around a 
drill press with an unusually long spindle 
travel. 

The M-56 fin was commonly used with the 



1 

Booster cup 

8 

KMNO4-MG puff cartridge 

2 

Booster pellet 

9 

Ignition cartridge 

3 

Interrupter plate 

10 

Fin (tail) for M-56 shell 


(lead, tetryl) 

11 

Primer 

4 

Fuze 

12 

Spacing washer 

5 

Fuze rotor 

13 

Increment holder 

6 

Detonator 

14 

Smokeless powder incre- 

7 

M-43 shell 


ments 

Figure 35. Component parts of 81-mm mortar 


shell with VT fuze. 

M-43 shell body. To fit the fin to the body, it 
was necessary to saw off the first two threads 
from the fin and insert a spacing washer of 
y 16 in. thick aluminum between the shell and 



Figure 36. 81-mm shell with VT fuze assem- 

bled. 

the fin. The shell was then completely assembled 
with the smoke puff cartridge inserted and the 
VT fuze screwed into place. After the weight 
of the shell, the number of the round, and the 
serial number of the fuze had been recorded, 


the shell was ready for delivery to the gun 
position. 

Gun Position 

The mortar was set up (Figure 40) and 


500 400 400 



Figure 37. Circuit diagram of rotor tester. 

aimed in accordance with the instructions 
given in the Basic Field Manual for this par- 
ticular gun. Information as to elevation and 
point of aim were furnished the gunner from 





Figure 38. Fixture for holding loaded rotor. 

the test request and weather data taken prior 
to firing. The cage on which the solenoid coils 
(used in muzzle velocity measurements) were 
mounted was adjusted so that the axes of the 


THE FIELD TESTING OF MORTAR SHELL FUZES 


345 


coils coincided with the axis of the gun. The 
cage was adjusted to the same elevation as the 
gun (Figure 41) and then shifted in a hori- 
zonal plane until the axes coincided. 

The person operating the electronic timing 


and the range, the height of function was 
readily obtained. 

In addition to the apparatus mentioned above, 



Figure 39. Rotor testing meter and jig. 

device (Figure 42) for measuring muzzle 
velocity also operated a battery command [BC] 
telescope at the gun position. The BC telescope 
was often used to get a quick check on heights 



Figure 41. Solenoid coils used for measuring 
muzzle velocity. 


a clock and blackboard were located at the gun 
position (Figure 32) and photographed from 
T i between rounds. The information on the 



Figure 40. Mortar shown in position for firing. 

of function. It had a vertical mil scale on which 
the angle between the smoke puff (or flash) 
and the splash could be read. From these data 


Figure 42. Electronic timing device for meas- 
uring muzzle velocity. 

blackboard was changed from round to round 
by the same operator who handled the muzzle 
velocity apparatus. A detailed description of 



346 


FIELD TESTING OF PROXIMITY FUZES 



the muzzle velocity measuring mechanism is 
given in reference 41. 

Each shell, after inspection, was magnetized 
so that it would actuate the muzzle velocity 
apparatus by inserting it in the magnetizing 
coil (Figure 43). The shell was then placed in 


Figure 43. Shell being magnetized in magnet- 
ization coil. 

the special release mechanism (Figure 44) and 
the mechanism placed on the mortar barrel 
(Figure 45) . This device enabled the operator to 
drop the shell down the mortar barrel by pulling 
a string from behind the concrete barricade 
(see Figures 40 and 42) . The gun operator was 
then ready to ask for clearance from the T i 
tower. 

The gun operator was responsible for watch- 
ing the early flight of the shell so as to note any 
unusual behavior such as excessive yaw or 
tumbling. The second operator recorded the 
muzzle velocity, time of flight of the round, and 
obtained the mil height of function in the BC 
telescope. While the gun operator magnetized 
the next round and placed it in position to be 
fired, the second operator recorded the firing 
point data and inserted the serial numbers for 
the next round on the blackboard. 


Ballistics Data 

The purpose of this discussion is to explain 
the method of measurement of the data, the 
method of calculation of the point of function, 
and the accuracy to be expected from the 


Figure 44. Shell being placed in special release 
mechanism. 

methods and apparatus used. It was desirable 
to know with a fair degree of accuracy the 
point of function or point of impact of each 
round. This information was necessary to 
determine the range and deflection of the 
round and the height of functioning of the unit. 
The point of function was located in the event 
of proper functions ; the point of impact in the 
case of duds. The point of function will be used 
here to include both cases. 

Method of Taking Measurements. Figure 46 
shows the location of the four towers, the gun 
position, and the line of reference. Each of the 
four towers had at least one aiming circle which 
was used to measure the azimuth of the point 
of function. The aiming circle is a device 
similar to the transit : its calibration is in mils ; 
its field is approximately 85 mils in radius, its 
magnification 4 to 1 ; and its turning angle is 
360 degrees or 6,400 mils (a mil on the aiming 
circle is defined as 1/6,400 of a circle). The 
scale of the aiming circle was in the field of 
view, the azimuth of the point of function of 


THE FIELD TESTING OF MORTAR SHELL FUZES 


347 


the round, with respect to the center of a scale 
located in the field of view, was read at the 
time of function. The reading thus obtained 
was added to or subtracted from the angle of 
the setting of the aiming circle, depending upon 
whether the point fell to the right or left of the 
center line. Since the area of view from the 
aiming circles was small for points of func- 
tion near the observation towers, it was at 
times necessary to employ two overlapping aim- 
ing circles in order to locate all of the points 
of function. 

The zero setting of the aiming circle at Ti 
tower was along the line from the to the T 2 



Figure 45. Shell and release mechanism being 
placed on mortar barrel. 

tower, and the center of the aiming circle was 
moved clockwise 328 mils to lie along the 
reference line. The zero settings of the aiming 
circles at T 2 , T 3 , and T 4 towers were along the 
line from these towers to T x tower. The azimuth 
of the point of function of the round was 
measured from these zero settings in a clock- 
wise direction. 

Method of Computation. The following 
symbols are used in explaining the method of 
making computations and analyzing the errors 
involved : 

|3 = angle in mils between line of aim and 
reference line. 



Figure 46. Sketch of Clinton Field Station, 
showing line of reference and position of obser- 
vation towers and gun. 


a = angle in mils measured at T 1 tower 
from the reference line to the point of 
function. Both a and (3 were positive if 
measured to the right of the reference 
line and negative if measured to the 
left. 

T 4 = 328 + a in mils, which is the angle be- 
tween line of Ti and T 2 towers and 
point of function. 

T i — angle in mils at T x tower measured 
clockwise from T 4 tower to point of 
function ( i = 2, 3, 4). 

AT. = indicates the amount of error of meas- 
urement, in mils, of the angles T { (i = 
1, 2, 3, 4). 


348 


FIELD TESTING OF PROXIMITY FUZES 




I SECRKT 


|inwmti t|<ittl uH| 1 1 1 i |iiti|i m|nn| i n i | n 1 1 1 1 1 n 1 1 H )- | 1 1 m | i|i ? m *t m 1 1 1 P 1 1 1 1 IM * 1 t f H H M H 1 1 1 1 j 1 * 1 1 i tntfi i i|tiii|iiii | i n i|ii n| ii u | H i | 

4800 4400 4200 4000 3900 3800 3700 3650 3600 3550 3500 3450 3400 3550 3320 3300 


THE FIELD TESTING OF MORTAR SHELL FUZES 


349 


TiF — the average of two calculations of the 
distance in feet from tower to the 
point of function, in case of discrepancy 
giving greatest weight to the calcula- 
tion using the angle measured at the 
tower nearest to the point of function. 
T 1 F i = the distance in feet from T i tower to 
point of function, calculated using 
angles and T i (i = 2, 3, 4). 

R = range of the round in feet, i.e., the dis- 
tance from gun position to point of 
function. 

T\Fi — the distance in feet from T t tower to 
point of function of the round, calcu- 
lated using the angles measured at Ti 
and T i towers (i — 2, 3, 4) . 

Knowing the angles T± and T { ( i = 2, 3, or 4) 
and the distance from T 4 to T if the distance 
from Ti to the point of function of the round 
was calculated by use of the law of sines. Since 
the angle T 2 and T 3 , or angles T 3 and T 4 were 
always obtained, there were two calculations 
for each point of function to check against each 
other. Similarly, T 2 F ly T 3 F 1} T 4 Fi were calcu- 
lated by use of the law of sines. 

A nomograph was constructed to solve the 
trigonometric relations between the above 
terms. Figure 47 exhibits the nomograph used. 
The final distance T 4 F was given as the average 
of TiF 2 and T X F 3 or of TiF 3 and 7\F 4 , giving 
greatest weight to the value calculated with the 
data from the tower nearest the point of func- 
tion. 

The range R of the round in feet was then 
calculated from the following equation : 

R = TiF — 150, 

where 150 was the distance in feet from the T 4 
tower to the gun position, and lay along the 
line of reference. 

The deflection D of the round in feet was the 
perpendicular distance from the point of func- 
tion to the line of aim. This distance in feet 
was given by the approximate formula : 

D = TiF (a — (3) . 

Errors to Be Expected. There were several 
factors affecting the accuracy of measurement 


of the point of function. The influence of these 
on the range of the shell is discussed below. 

1. Errors in measurements of the locations 
of the various towers. These points were sur- 
veyed by a professional surveyor, and the meas- 
urements were checked carefully. It was felt 
that errors from this source were negligible. 

2. Errors in measurement of angles at the 
various towers. These angles could be measured 
with an error of ±1 mil. Figure 48 shows 



Figure 48. Graph showing errors in com- 
puted distance from T\ tower to point of func- 
tion for errors of 1 mil in angles measured at 
various observation towers. 

graphs of the errors in FiF 2 , T 4 F 3 , and 7\F 4 
to be expected when errors of 1 mil were made 
in measuring the various angles. Inspection of 
these graphs shows that by using the data from 
the proper towers, the maximum error in the 
distance from Ti tower to the point of function 
for ranges from 1,000 to 12,000 ft is 13 ft. 

3. There was also an error in subtracting 150 
ft from the distance T ± F in order to get the 
range of the round, unless the point of function 
fell along the line of reference. This error is 
equal to 150 X sin a. Since a is a small angle, 
the error from this source is insignificant. 

4. The size of the nomograph constructed to 
solve the equations was 24x36 in. Calculations 
using this nomograph should be more accurate 
than calculations using the conventional 10-in. 
slide rule. Calculations showed that the nomo- 


SECRE' 


350 


FIELD TESTING OF PROXIMITY FUZES 


graph could be read with an error of less than 
5 ft. 

5. The method of calculating the deflection 
was approximate, since the assumption was that 
the sine of the angle (a — (3) equaled the angle. 
This was nearly true, since the angle was small. 
Errors in measuring the angles a and (3 would 
also result in an error in calculating the deflec- 
tion. Using an estimated measurement accuracy 
of 1 mil, the maximum error in the angle 
(a — (3) would be 2 mils. This would result in a 



Figure 49. Houston film developer, Model 11, 
Type K-3 in use. 


maximum error of approximately 2 ft per 
thousand feet of range. 

Method of Obtaining Heights of Function 

The height of function of the VT fuze was 
determined by measuring the enlarged image 
of a 16-mm motion picture film. Pictures were 
taken from three positions: one behind the 
firing point and two along the line of flight of 
the shell. Bell and Howell Filmo Cameras, 
Model 70-DA, were used, operating at maximum 
speed of 64 frames per second. The camera at 
the Ti tower pointed along the flight line and 
was equipped with a 4-in. telephoto lens. At 
the other two stations a 2-in. lens was used 
unless the camera was pointed at a small enough 
angle to the flight line to insure the function 
being in a small field of view, in which case a 
4-in. lens was used. The cameras were also 
equipped with 1-in. lenses for photographing 


(after each function) a blackboard giving the 
round and fuze number. The operators started 
the cameras for photographing functions when 
the signal “camera” was given by the operator 
in charge. This signal was given approximately 
2 sec before the estimated functioning time. 

The film was processed with a Houston Film 
Developer, Model 11, Type K-3. Best results 
were obtained by following the procedure in 
reference 48. Ansco Hypan film was used. Fig- 
ure 49 shows the film being processed in the 
Houston Developer. 

The Recordak Film Reader, Model C, was 
used to obtain an enlarged image of the finished 
film. The image was measured to the nearest 
0.02 in. Magnification of the image was care- 
fully checked by measuring the height of known 
objects at known distances. Since the focal 
length of the lens and the distance from camera 
to function were known, the height of function 
was computed, using the formula, 

Height of function = 

Measured height of image X distance to function 
Focal length X K 

where K is the magnification of the image. This 
formula is accurate to 1 ft at a range of 4,400 
ft. There was always at least one camera sta- 
tion within this range. Hence the accuracy was 
consistently within a foot of the height of 
function if the picture showed the actual height 
of function. 

Fuze Flight Performance 

A block diagram of the radio equipment is 
shown in Figure 50. 



Figure 50. Block diagram of radio apparatus. 


A Zenith broad band receiver with a flat 
frequency response of ±3 me was used. Two 
dipole antennas were connected by 50-ohm 
transmission lines to the receiver. One antenna 
was used for the Globe-Union units, the other 
for Zenith units. A Hewlett-Packard Model 




THE FIELD TESTING OF MORTAR SHELL FUZES 


351 


200C audio oscillator supplied the 1,000-c note 
used to obtain zero time. This 1,000-c note was 
shut off at the gun position by a switch actuated 
by muzzle blast from the gun. A mixer amplifier 
fed both the 1,000-c note and the signal from 
the receiver into the network at the same time. 
This unit had very little gain and was used 
primarily for mixing. A limiter, designed to 
keep the signal at a constant level, was coupled 
as shown to the Presto 8-K recorder. A micro- 
phone connected into the recorder circuit made 
possible the recording of voice announcements 
associated with the firing of each round. All 
recordings were made with a sapphire cutting 
needle on Audiodisks. Before firing a given 
round, the receiver was tuned to the expected 
frequency of the unit listed on the test request 
data sheet. 

Coordinating the radio with the firing oper- 
ation was carried out as follows. As the gun 
operator began counting, the man at the tele- 
phone in the radio laboratory counted aloud in 
unison with him. This gave the other operator 
time to start recording the 1,000-c note. As the 
shot was fired, the note was cut off sharply by 
the micro switch and the signal from the unit 
cut in. The termination of the 1,000-c note gave 
the zero time for the signal being recorded. A 
check was kept on the relative strength of the 
signal by observing the monitoring meter on 
the recorder, designating the optimum signal 
strength by the number 5. The volume of the 
1,000-c note was always set to 4. The quality 
of the signal was determined by ear, again des- 
ignating by 5 the optimum quality. Both read- 
ings were recorded on a data sheet for each 
round. The radio operator timed the duration 
of the signal with a stopwatch and at the end 
of each signal recorded the round number on 
the disk. 

Determination of Generator Speed. To record 
generator frequency, the signal received from 
the fuze was fed to the horizontal plates of an 
oscilloscope. The vertical plates were tied to- 
gether and grounded. Best results were ob- 
tained by picking up the signal from the moni- 
tor of the recorder. The oscilloscope was then 
photographed with a Bell and Howell, Model 
70-DA, 16-mm motion picture camera from 
which the shutter mechanism had been re- 


moved and the spring drive replaced by a syn- 
chronous motor giving a film speed of 15 in. 
per sec. The camera and oscilloscope were en- 
closed in a dark chamber. 

Approximately a second before the shell was 
fired, the camera was started. The 1,000-c note 
from the audio oscillator was recorded until the 
firing of the mortar operated the zero time de- 
vice. The generator frequency was recorded on 
the film from this time until the functioning of 
the fuze. 

Ansco Triple S Pan and Eastman Super XX 
films were found to be the most easily read. 
After processing, the films were marked at 15 
in. intervals in order that readings could be 
taken every second. Readings were also taken 
at three points in the first second, since the 
speed changed rapidly immediately after the 
shell was fired. Reading of the films was done 
on the Recordak Film Reader, Model C. Since 
the generator had six poles, the generator speed 
equals % of the frequency. 

Although the equipment operated well, the 
system was not completely satisfactory. The 
1,000-c note was used as a standard to check 
the apparatus and results were consistently 
very good. However, the carrier from the fuze 
was modulated by the plate voltage ripple and 
also by the filament voltage. The filament modu- 
lation gave the fundamental frequency and the 
plate voltage ripple gave the first harmonic. 
During the flight of the shell, the predominate 
modulation was first the filament voltage, then 
the plate voltage ripple, and finally the filament 
voltage again at the end of the trajectory. 
Hence, extreme care had to be taken to avoid 
confusing the fundamentals with the harmonic. 
Reporter units should have been used when ac- 
curate generator speeds were needed. 

Carrier modulation was also recorded on 
phonograph records which were analyzed by 
a method described in the Bibliography. 13 

Weather Data 

The purpose of collecting weather data was 
to obtain information pertinent to ballistic cal- 
culations and also to determine any adverse 
effects of weather on the VT fuze. 

The direction and velocity of the surface 
wind were determined, respectively, by a wind 


SECRET 


352 


FIELD TESTING OF PROXIMITY FUZES 


vane and an anemometer. To determine wind at 
higher altitudes, a pilot balloon was released 
each hour during firing and theodolite readings 
taken on the position of the balloon. Reference 
47 was used to convert these readings to an 
average wind for each 1,000-ft zone. A ballistic 
wind was then calculated by averaging these 
zone winds weighted as to the time the projec- 
tile was in each zone. Although no attempt had 
been made to correct the ballistic data for wind, 
the recorded ballistic wind could have been used 
for this purpose. 

The sky condition was recorded as overcast, 
broken, scattered, or clear, depending on 
whether the coverage of the sky was over 0.9, 
between 0.5 and 0.9, between 0.1 and 0.5, or less 
than 0.1, respectively. Standard weather bureau 
terminology was used to describe cloud types. 

Continuous daily recording of temperature, 
atmospheric pressure, and humidity were made 
by thermograph, barograph, and hydrograph, 
respectively. Other pertinent weather informa- 
tion, such as fog and precipitation, were also 
recorded. 

Field Test Reports 

Immediately after a firing program was com- 
pleted or at intervals during long programs, 
data from the field were brought into the office 
in Clinton and given to the computing group. 
These raw data were then transcribed into a 
calculation sheet. 

Rounds fired were numbered consecutively, 
and these round numbers were used to coordi- 
nate all data. Data sheets were furnished to 
the loading department, the gun station, radio 
operators, and tower observers for recording 
such information as the type of vehicle and 
fuze, weight of complete round, charge, angle 
of elevation, type of function, time of func- 
tion, azimuth of function, strength and quality 
of radio signal, and muzzle velocity. Specially 
prepared forms were used to record the data 
at the field. 

A calculation sheet was made up to be used 
with the nomograph described in the discussion 
of ballistic data given in this section. On this 
sheet, the columns were arranged to allow 
orderly recording of the data for rapid com- 
putation. 


When the calculations were completed, they 
were recorded on a field test report sheet. This 
sheet contained the results of the test in a 
compact form and included the principal data 
submitted in the Field Test Reports. As used in 
this report, the mean dispersion of a group of 
variables was defined as the average of absolute 
values of the differences between the mean 
value of the variables and the particular vari- 
ables. 

The request for field tests included the fol- 
lowing information: (1) originator of the test; 
(2) the contact person representing the origi- 
nator; (3) purpose of test ; (4) description and 
conditions of test; (5) description of material 
to be tested; (6) data required from the test; 
(7) source of material ; (8) urgency of test ; (9) 
relation of other test requests; (10) statement 
as to whether originator's representative would 
witness the test; (11) remarks; (12) approval 
of test request by originator; (13) approval or 
modification of test request by the director of 
the field station. 

Immediately upon receipt of a test request, 
one person was assigned to study the test re- 
quest and begin writing as much of the report 
as was possible before the data were obtained 
from the field station. This was necessary in 
order to facilitate sending reports out on the 
day the firing was done. 


8.4.4 TJ ie Mathematical Calculation of 
Mortar Shell Trajectories 

Three methods for the computation of mor- 
tar shell trajectories 45 were considered, namely, 
the Piton-Bressant procedure, a method espe- 
cially adapted to the use of the quadratic air- 
resistance law, and the method of numerical 
integration as developed in 1918 and the fol- 
lowing few years. It was found that existing 
ballistic tables were inapplicable to the par- 
ticular type of mortar shell in question, since 
the tables give trajectories only for shells 
whose ballistic coefficients are greater than or 
equal to unity while these mortar shells have 
ballistic coefficients of one-half or less. 

The Piton-Bressant method requires a 
knowledge of the initial conditions, that is, 


SECRET 


THE FIELD TESTING OF MORTAR SHELL FUZES 


353 


muzzle velocity and elevation of the mortar, 
and of the range on the horizontal. This method 
is the easiest of the three to apply, but it is sub- 
ject to an inherent error of a magnitude indi- 
cated by Figure 51. No particular assumption 
is made about air resistance, the effect of which 
is taken into account by the use made of the 
measured range. The method permits the calcu- 
lation of as many points on the trajectory as 
may be desired, together with the time at each. 

In the second method, it is assumed that the 



Figure 51. Comparison of trajectory calculated 
by Piton-Bressant procedure with exact tra- 
jectory. 


drag of the air is given by the expression cv 2 , 
where v is the velocity of the shell at any time 
and c is a constant whose value must be found 
from field or wind tunnel measurements. For- 
mulas were developed giving the coordinates 
and time as functions of the inclination. By 
means of these formulas, as many points on the 
trajectory can be calculated as may be desired, 
together with the time at each. This method is 
capable of as much accuracy as the measured 
data warrant. It was this method which was 
used in calculating the “exact trajectory” of 
the figure. 

Since the type of mortar shell under consid- 
eration has a ballistic coefficient less than unity 
(corresponding to a relatively large air re- 
sistance), the effect caused by the decrease in 
air density with increasing height may be 
appreciable on the trajectory as a whole. In 
order to test this point the trajectory for a 
muzzle velocity of 635 fps, an elevation of the 


mortar of 65 degrees, and a ballistic coefficient 
of 0.4284 b was calculated by the method of 
numerical integration using the tabulated 
Gavre function first with account taken of the 
change in air density with changing altitude 
and then ignoring this change. The respective 
ranges were found to be 5,033 and 4,901 ft. 
The difference is 132 ft, or about 2.6 per cent 
of the range. 

Formulas were developed for the effects pro- 
duced by small changes in initial conditions. 
The method of differentials was used in this 
connection. Application of these formulas was 
made to the problem of the effect of wind on a 
trajectory. 46 


8 4 5 Photographing Height of Function 
of VT Fuze 

Introduction 

Experiments were performed for the pur- 
pose of gaining more definite information on 
the measurements of heights of function of the 
VT fuze. The heights of function were calcu- 
lated from photographic data taken at three 
observation towers. To obtain the actual height 
at which the VT fuze functioned, it was desir- 
able to photograph the detonation of the tetryl 
in the fuze ; this was the first indication of the 
functioning of the fuze. During a certain pe- 
riod, when potassium permanganate and mag- 
nesium packs were not available to be placed 
behind the tetryl pellet to make a puff after the 
fuze functioned, black powder was employed 
for this purpose. The functioning of approxi- 
mately two hundred of the fuzes was photo- 
graphed at this time by three cameras operat- 
ing at 64 frames per second, and in no instance 
did a flash appear on any of the films. Three 
fuzes were then placed in the mortar shells in 
the usual manner, except that the black powder 
was missing, and were statically detonated. 
Again, a flash was not recorded on any one of 
the films. Hence, it was assumed that when 
potassium permanganate and magnesium puffs 
were used, the flash appearing on the film was 
actually from the potassium permanganate 

b Approximately the value for the M-43C shell with 
the T-132 fuze. 


SECRET 


354 


FIELD TESTING OF PROXIMITY FUZES 


and magnesium and not from the tetryl pellet. 
Potassium permanganate and magnesium was 
used thereafter for making the puff, and a flash 
appeared on the film for each proper function. 

The disagreement between the heights of 
function obtained from the photographs from 
the three towers was greater than 1 ft in only 3 
per cent of the cases and was never greater 
than 2 ft. Thus, the method of measuring the 
heights of the puffs seemed to be quite accu- 
rate. 

Experiments to Determine Whether 
Actual Heights of Function Were 
Being Photographed 

Experiment I. The first evidence of function 
should be the detonation of the tetryl booster 
pellet. To discover if this detonation was ca- 
pable of being photographed, 10 tetryl booster 
pellets were statically detonated by taping each 
pellet to an electric detonator and fired by 
means of a hand magneto. Motion pictures 
taken at 64 frames per sec showed a definite 
flash. The explosions were also photographed 
by a shutterless motor-driven camera. Meas- 
urement of the length of a bright streak on the 
finished film from this camera showed the dura- 
tion of flash to be 0.02 sec. 

Experiment II. Three M-43 inert loaded 
shells were loaded with detonator and tetryl 
booster pellet only. The tetryl was held in the 
aluminum tetryl cup in a standard M-53 PD 
fuze. These units were detonated statically as 
in experiment I and photographed with three 
cameras operating simultaneously. Photo- 
graphic data showed a brilliant flash with an 
average duration of 0.18 sec. The flash was 
followed by a thin gray smoke. 

Experiment III. Three M-43 inert loaded 
shells were packed with detonator and tetryl 
pellet. The tetryl was held in a brass tetryl cup 
in a reject VT fuze. The units were statically 
detonated and photographed with three cam- 
eras. There was no evidence of a flash on the 
finished film. A dense black smoke was the first 
visible record of function. This possibly indi- 
cated that the flash seen in using tetryl packed 
in aluminum cups may have come from the 
burning aluminum. The flash seen in the case 
of tetryl alone was not present when the tetryl 


was packed in brass, possibly because the 
energy from the detonation was used in break- 
ing and heating the shell. 

Experiment IV. Eighteen units were loaded 
as in experiment III and fired from the stand- 
ard 81-mm M-l mortar. There was no evidence 
of a flash when the functioning of these units 
was photographed by three cameras. However, 
smoke was plainly visible on the films. 

Experiment V. Units loaded with a black 
powder cartridge behind the tetryl cup showed 
smoke as the first visible evidence of function. 
In photographs of 200 units packed with the 
black powder cartridge, there was no record of 
a flash. 

Experiment VI. Shells were ordinarily 
packed with a cartridge of potassium perman- 
ganate and magnesium behind the booster pel- 
let. The functioning of this round photographed 
nicely as a black point topped or surrounded 
by a flash. The flash was found to photograph 
well against a water background in all types of 
weather. Considering the above experiments, 
the conclusion is drawn that this flash was 
caused by the potassium permanganate and 
magnesium and not by the tetryl pellet. A com- 
plete account of the preceding experiments to- 
gether with photographs may be found in ref- 
erence 43. Comparisons of black powder and 
permanganate-magnesium spotting charges are 
also reported in reference 23. 

Comparison of Heights of Function 
Obtained from Three Observation 
Towers 

The shutter on the cameras used in photo- 
graphing the functioning of the VT fuze had 
an opening of 204 degrees. When operating at 
64 frames per sec, the shutter was open 0.0088 
sec and then closed 0.0068 sec. Hence, the shut- 
ter was open approximately % of the time and 
closed % of the time. With three cameras oper- 
ating essentially independently of one another, 
the probability of missing the first evidence of 
function was (%) 3 , or approximately Yli- If 
the shell had a maximum approach velocity of 
500 fps, it might have traveled as much as 3.4 
ft while the shutter on one of the cameras was 
closed. Since agreement among three camera 
stations was consistently within a foot, it seems 


SECRET 


THE FIELD TESTING OF MORTAR SHELL FUZES 


355 


unlikely that the explosion was carried down- 
ward with the same velocity as the shell. Any 
error larger than a foot between readings was 


point. Since the cameras were operating inde- 
pendently, the detonation might have taken 
place while one or more of the camera shut- 


braze wires 
TO CONTAINER 



1 . 

Cable guide 

6. 

Steel tube 

2. 

Steel cable 

7. 

Base plate 

3. 

Shear pin 

8. 

Threaded base 

4. 

Cover 

9. 

Set screw 

5. 

Stud for shear pin 

10. 

Time fuze 


11. Parachute space 


Figure 52. Type A-l mortar shell retrieving device. 


invariably the result of faulty measuring or 
computing. 

Measurements were taken from the highest 
point from which the explosion appeared to 
emanate to the water below the functioning 


ters were closed. However, the close agreement 
of data from the three cameras indicated 
that the point of function remained fixed and 
visible for a sufficient length of time to be re- 
corded photographically in all three cases. 


i 


SECRET 


i 


356 


FIELD TESTING OF PROXIMITY FUZES 


Furthermore, this close agreement seemed to 
substantiate the fact that the results were accu- 
rate. The only error present may have been the 
result of the time lapse between the functioning 
of the fuze and the appearance of visible evi- 
dence of it. Considering the fact that tetryl has 


Nor e- Use One Oram Base Char6_e 

1. Adapter for M-65 fuze 

2. Steel plate 

3. Internal steel tube (half cylinders) 

4. Shear pin 

5. Threaded base 

6. Time fuze 

Figure 53. Type A-2 mortar shell retrieving 
device. 

a rate of detonation of thousands of meters per 
second, the error introduced was less than 1 ft. 


846 Parachute Recovery Devices 
Introduction 

During the development of the VT mortar 
fuzes, it became apparent that some means was 
needed to allow the fuzes to be subjected to 



Figure 54. Type B fuze retrieving unit. 


accelerations comparable with the accelerations 
encountered in actual firing and still permit 
further testing and inspection of these fuzes. 
This was necessary so that damage to the fuze 
caused by acceleration might be studied and 
faulty or failing parts redesigned. The centri- 
fuge furnished a partial solution to the prob- 
lem. However, the accelerations available with 


the centrifuge did not accurately simulate the 
instantaneous acceleration encountered in ac- 
tual firing. It was agreed that some means for 
recovery of fuzes after they had actually been 
fired and gone through part of a normal flight 
was needed. The development of a recovery de- 
vice was assigned to the University of Iowa. 

Devices for parachute recovery not only of 
the VT fuzes but of complete 81-mm mortar 
shells were developed and put into production 
and use. On the whole, these devices functioned 
satisfactorily. The various types of devices, 
their applications and use will be discussed be- 
low. 44 

Type A-l Device 

The first device developed consisted of a 
tubular steel parachute container with 
threaded base. The threaded base was screwed 
into the mortar shell in the position normally 
occupied by the shell fuze. This device was in- 
tended for recovery of the complete projectile. 
A fuze or other material of interest could be 
mounted inside the shell body. The original de- 
sign (type A) proved unsatisfactory and was 
never used. 

Figure 52 is a drawing of the type A-l de- 
vice as used. Space was provided for a fixed 
time (15 sec) powder train fuze (M-65) to 
eject the parachute. The M-65 fuze was inserted 
in the bottom of the container and the para- 
chute was packed snugly against the fuze. The 
cover was placed over the parachute and held 
in position by three 0.081-in. half-hard brass 
shear pins. The cover was fastened securely to 
the container through two %-in. flexible steel 
cables. One end of each cable was brazed to the 
outside of the container. The other end of each 
cable was passed down through the top of the 
cover and back up through the cover from the 
bottom. The ends were then brazed to the top of 
the cover. A loop in the steel cables for attach- 
ment of the parachute shroud lines was left on 
the bottom side of the cover. 

In operation, the M-65 fuze was initiated 
when the shell was fired. After 15 sec of flight, 
the powder train ignited a reduced (approxi- 
mately 1 g) charge of black powder in the base 
of the fuze and forced the fuze forward; this 
sheared the pins retaining the cover and forced 




SECRET 


THE FIELD TESTING OF MORTAR SHELL FUZES 


357 


the parachute out. The whole shell was then 
recovered on the parachute. 

The principal difficulty encountered in the 
use of this device was separation of the steel 
cables from the container at the point where 
they were brazed. This difficulty was prac- 
tically eliminated by greater care not to over- 
heat the cables in brazing. At the Clinton Field 
Station, 80 of these devices were used to re- 


mounting the M-65 fuze to operate the device 
on the extreme front end of the assembly. The 
base charge of the M-65 fuze was used to shear 
half-hard brass pins and release the parachute. 
Figure 53 is a drawing of the type A-2 device. 

Type B Device 

The type B device was developed very soon 
after the type A device and was actually in pro- 



1 . 

Mortar shell 

6. 

Part from M-lll or M-lll A-2 

time fuze 

2. 

Steel housing 

7. 

Part from M-lll or M-lll A-2 

time fuze 

3. 

Part from M-lll or M-lll A-2 time fuze 

8. 

Part from M-lll or M-lll A-2 

time fuze 

4. 

Steel tube (half cylinders) 

9. 

Loop anchor for shroud lines 


5. 

Safety wire 

10. 

Shear pin 




11. Primer 


Figure 55. Type C fuze retrieving device. 


cover complete rounds of M-56 mortar shells. 
Of the 80 used, 61 functioned satisfactorily. 

Type A-2 Device 

The type A-2 device was never built, though 
drawings were prepared. It provided for secure 
fastening of the parachute shroud lines to the 
threaded base and eliminated the steel cables 
used on the type A-l device. Approximately the 
same size and shape container was used as for 
the type A-l device. Provision was made for 


duction first. It was built into a modified M-56 
mortar shell. This device provided for mount- 
ing the VT fuze in its normal position on the 
shell. 

The M-56 mortar shell was modified as fol- 
lows. The nose of the shell was cut off just for- 
ward of the three small bosses which touch the 
barrel (actually right at the line between the 
shell nose and the straight part of body). The 
inside of the shell body was reamed to a stand- 
ard size. A circular steel plate was pressed 


358 


FIELD TESTING OF PROXIMITY FUZES 


down inside the shell to a depth of approxi- 
mately 6 in. and secured by steel pins pressed 
through the shell wall and into the plate. The 
space forward of this steel plate was used for 
the parachute and an aluminum piston in which 
an M-65 powder train fuze was mounted. The 
nose was fastened back on the shell body with 
a short piece of steel tube pressed inside the 
nose and held to the body with 3 half-hard 
brass pins (0.081 in. in diameter). A loop of 
steel rod brazed to the nose served as an anchor 
point for the parachute shroud lines. The com- 
pleted device presented the same external ap- 
pearance as a standard M-56 shell. Figure 54 is 
a drawing of the type B device. 

When the shell was fired, the M-65 powder 
train fuze was initiated and the time ring 
began burning. After 15 sec of flight, the time 
ring ignited the base charge (reduced to 1 g) 
of black powder in the fuze. This forced the 
nose off and expelled the parachute. The nose 
with the VT fuze attached was brought down 
on the parachute. 

At the Clinton Field Station 45 of these de- 
vices were used. Of the 45 tried, 44 functioned 
satisfactorily. Several hundred of these devices 
were shipped to Blossom Point, where they also 
functioned satisfactorily. 

All of the parachutes for types A, A-l, A-2, 
and B devices were 36-in. Fortesan rayon cano- 
pies with 100-lb rayon shroud lines. Some of the 
canopies were white and some were dyed 
orange to make them easier to follow. 

Type C Device 

One objection to the type B device was that 
it was built into an M-56 mortar shell; conse- 
quently, it was impossible to subject the VT 
fuze to the accelerations desired. The design 
was such that it could not be adapted to the 
lighter M-43 shell with which the higher accel- 
erations might be realized. Therefore, develop- 
ment was begun on a completely new device 
which would work equally well in the M-56 or 
M-43 mortar shell. This device, designated as 
type C, was still in the development stage when 
operations were terminated. The type C device 
was a complete unit which might be inserted in 
either an M-56 or M-43 A-l empty shell after 
removal of the adapter ring in the shell nose. 


It provided for mounting the VT fuze in its 
normal position. After the type C device was 
inserted in either the M-56 or M-43 A-l mortar 
shell, the shell presented approximately the 
same external appearance as before. The device 
was built into a steel tube approximately 6 in. 
long and l 3 /4-in. inside diameter. Space was 
provided for an adjustable time mechanical 
time fuze, a parachute, and a nose ring with 
threads for the VT fuze. The time fuze used 
was actually part of two standard fuzes, the 
M-lll or M-lll A-2, and the M-136. The timing 
elements or clocks in these two fuzes were 
identical in external appearance and differed 
only in the rate at which the timing disk 
turned. The body of the M-lll fuze and the 
clock from the M-136 fuze were used. The hy- 
brid fuze thus made up was modified so that 
it was acceleration initiated instead of arming 
wire initiated as originally. The delayed arm- 
ing mechanism was removed completely. The 
parachute used was a 30-in. Bemberg rayon 
canopy with 40-lb rayon shroud lines. Figure 
55 is a drawing of the type C device. 

In operation the time fuze was initiated 
when the shell was fired, and the base charge 
was ignited at any desired time thereafter 
(time was adjustable from 5 to 30 sec). This 
forced the time fuze forward, pushed the nose 
ring off and expelled the parachute. The nose 
ring and the VT fuze were recovered on the 
parachute. 

At Clinton Field Station, 15 units were 
tested. Of the 15 tested, five functioned satis- 
factorily. 

Recovery Procedure 

In practice, rounds fired for recovery were 
fired at an elevation of 75 to 80 degrees so that 
the shell would be traveling slowly when the 
parachute opened. Actual recovery of shells or 
fuzes was somewhat complicated by the fact 
that firing was done over water and recovery 
was by boat. 

Ordinarily two boats were sent out. They 
stood by out of the line of fire until after the 
parachute opened. Usually the men in the boats 
could see the parachute open and get into posi- 
tion to pick it up very soon after it hit the 
water. When the men in the boat did not see the 


SECRET 


THE FIELD TESTING OF MORTAR SHELL FUZES 


359 


parachute, flag signals from shore were used to 
direct the boats toward the point where the 
parachute was expected to fall. 

Usually the parachute hit in such a manner 
as to trap air between the water and the 



Figure 56. Breech-loading mortar, 81 mm. 


canopy and remained afloat for several min- 
utes. If the parachute sank, aiming circle bear- 
ings from two towers ( T x and To ) were taken 
on the point where parachutes sank. Use was 
made of these data to recover several shells 
which otherwise would have been lost. On some 


occasions the wind was such that the para- 
chutes were carried over land. This made re- 
covery much less difficult. In fact, some were 
blown back to the firing point and were caught 
without striking the ground. 

Recovered fuzes were dried as thoroughly as 
possible with warm air blasts before being re- 
turned to the interested parties for examina- 
tion. 


847 Recovery by Use of Breech-Loading 
Mortar 

The firing of shells into a rectangular trough 
filled with cotton waste was another very satis- 
factory method of recovery. The horizontal 
breech-loading mortar, shown in Figure 56, 
was used. The trough was 20 ft long. The con- 
struction of a metal detector for use in locat- 
ing the shell within the trough was considered 
but was found to be unnecessary. The heat de- 
veloped within the waste proved to be a suffi- 
cient indicator of the trajectory of the shell 
within the waste for rapid recovery by hand. 


SECRET 


Chapter 9 

ANALYSIS OF PERFORMANCE 


91 INTRODUCTION 

911 Purpose 

I T is the purpose of this chapter to present 
an analysis of the performance of variable- 
time [VT] fuzes based on results obtained 
mainly by those methods of field testing de- 
scribed in the preceding chapter. Where pos- 
sible, these results are compared with predic- 
tions of performance based on the theory of 
operation of the fuzes and on the characteris- 
tics of the fuzes obtained in the laboratory 
described in earlier chapters. 


9,1,2 Sources of Data 

Classification of Tests 

Data on the field performance of the fuzes 
are not limited to the proving grounds or meth- 
ods described in Chapter 8. As pointed out in 
Chapter 5, valuable data were obtained through 
the courtesy of various military agencies. Field 
tests may be classified roughly as follows: 

1. Experimental tests performed during the 
course of development of a fuze. For any fuze 
that reached the mass production stage, the 
results of development tests are of no more 
than historical interest and are not given here. 

2. Acceptance tests. For many fuzes, the 
acceptance tests performed by Army Ordnance 
provide voluminous data obtained under stand- 
ardized test conditions. The conditions of the 
acceptance tests are described in an appendix 
to this chapter, and considerable use is made of 

a This chapter was prepared by T. N. White, Jr., with 
the assistance of Rachel Vorkink, Alan Leiner, and 
Gladys Rabinow, Ordnance Development Division, Na- 
tional Bureau of Standards, and Paul F. Bartunek, 
Rosemarie Kilker, and David Fisher. In addition, H. F. 
Stimson, of the Heat and Power Division, National 
Bureau of Standards, prepared the sections dealing with 
afterburning, and Walter G. Finch, former captain 
in the VT Fuze Detachment of the Ordnance Depart- 
ment, prepared Section 9.6 on operational use. Captain 
Finch is now a graduate student at Johns Hopkins Uni- 
versity. The summary, Section 9.7, was prepared by the 
editor. 


the results under the title, “Performance under 
Acceptance Test Conditions,” in various sec- 
tions of the chapter. 

3. Experimental tests performed with pro- 
duction fuzes or with fuzes closely approxi- 
mating production design. These tests are of 
particular interest in that they include experi- 
ments to determine fuze performance under 
various conditions that are of importance in 
Service use but which are different from the 
acceptance test conditions. In addition to tests 
performed at the proving grounds, described in 
Chapter 8, this category includes certain im- 
portant Service tests performed by military 
proving grounds. 

The results of the above types of tests are 
given in the various sections of this chapter 
where the performance of the pertinent fuze is 
under discussion. Reports on the results of com- 
bat operations with VT fuzes are summarized 
in a separate section. As would be expected, 
these important results are of a qualitative 
nature, mostly statements of the judgment of 
observers working under very difficult condi- 
tions. Such results are not susceptible to quan- 
titative analysis, and no attempt was made to 
subject them to such treatment. 

Test Reference System 

The inclusion of round-by-round results even 
in the microfilm supplement of this report is 
impractical. Reports on approximately 2,000 
tests were prepared by the Ordnance Develop- 
ment Division of the National Bureau of Stand- 
ards alone. There is, therefore, included in the 
microfilm supplement a set of tabular sum- 
maries of the results of individual tests identi- 
fied by test number, and reference is made to 
these test numbers to show the sources of the 
data presented in the text. These summaries 
give the most important conditions of each test, 
and also references to the detailed report on 
each test. (Such summaries are not available 
for Army rocket fuze tests ; in this case, refer- 
ence is made directly to the detailed report in 
order to give positive identification of the 


360 


| SECRET 


INTRODUCTION 


361 


source material.) Some of these summaries 
cover tests performed by military agencies, and 
in some cases the data were provided through 
courtesy of the military agency in advance of 
the official report of the agency. In all cases 
where an official report was available, refer- 
ence is given to the official report. Every effort 
has been made to attain accuracy in these sum- 
maries, but it should be understood that there 
is no implication that the military agencies con- 
cerned are in any way bound by the results 
given or by the interpretation of the results 
presented in this report. 


9,1,3 Description of Performance 

The ideal representation of the perform- 
ance of a fuze would be a diagram or model 
showing the frequency of bursts in space under 
each testing condition. A schematic one-dimen- 
sional representation is shown in Figure 1. 
This diagram is typical of bomb fuze perform- 



Figure 1 . Schematic distribution of VT fuze 
functions along trajectory. 


ance, except that the region of proper func- 
tions has been expanded greatly (relative to the 
total length of trajectory) in order to show 
better the form of the proper function distri- 
bution. 

The data from most tests were much too 
limited to yield a representative frequency dis- 
tribution. The bursts that occurred in each test 
were therefore classified as proper, early, dud, 
etc., according to the position or time of oc- 
currence. This method gave the score of the 
test. For certain classes of burst, particularly 
the proper bursts, the average position and 
some measure of scatter were usually esti- 
mated. 


Test programs such as acceptance tests, 
which yielded large masses of data, showed 
that there was no sharp dividing line between 
the different classes of burst. It was not always 
possible even to distinguish between a burst at 
the end of the flight and a dud. The method of 
classification of bursts was therefore to some 
extent arbitrary. For practical purposes this 
uncertainty is a matter for little concern. In- 
spection of Figure 1 shows that the proper 
burst score, which is the most important score, 
is little affected by the position of the limits 
within which bursts are classed as proper, pro- 
vided these limits are placed well out on the 
“tails” of the proper burst “hump.” Generally 
speaking, there was rarely any serious diffi- 
culty in distinguishing between proper func- 
tions and malfunctions, except in the very 
earliest stages of testing of a basically new 
fuze. 

In the foregoing discussion it is tacitly as- 
sumed that a function should be classed as 
proper if the function is due primarily to in- 
teraction between the fuze and the target. In 
general, this is the criterion that was used in 
experimental testing. There is, however, an- 
other criterion that was used to some extent in 
acceptance testing. This criterion is derived 
from an assumption as to the space limits with- 
in which an air burst may be regarded as useful 
in inflicting damage in Service applications. In 
a few cases the limits so set were a little severe 
and were later broadened. The effect of such 
changes on aggregate acceptance test scores 
was, however, practically nil, and no attempt 
has been made to revise old scores in order to 
reduce all to a rigorously equal basis. It is also 
true that the differences between the two cri- 
teria mentioned above had a negligible effect on 
the estimates of performance. 

Throughout this chapter, the terms burst and 
function are used interchangeably, as is the 
case in most of the reports of the Division 4 
NDRC Central Laboratory, and it is only in 
rare instances that there is any important dis- 
tinction between the two. However, for the sake 
of exactness it appears worth while to empha- 
size that it is the position of a flash or smoke 
from a spotting charge or high-explosive [HE] 
load that is actually estimated. The position at 



362 


ANALYSIS OF PERFORMANCE 


which the fuze functions cannot be measured 
directly in dynamic tests. 

914 Evaluation by Field and 

Laboratory Testing 

Before considering the results of field tests, 
it is important to realize that the evaluation 
of any particular fuze design was not based 
solely on its field performance, although satis- 
factory field performance was essential to the 
final acceptance of a design. Dependence on 
laboratory data was particularly important for 
fuzes in the earlier stages of development. It 
is safe to say that if it had been essential to 
obtain statistically convincing proof of the 
value of every design change by means of field 
tests, very few fuzes would have reached the 
production stage during World War II. The 
success of each fuze development was depend- 
ent on the soundness of the engineering theory 
of action of the fuze (which involved various 
simplifying assumptions), the validity of labo- 
ratory testing conditions (which could only 
approximate field conditions), and field testing 
(which was limited by both the time and labor 
required to build fuzes, and by difficulties in 
duplicating service conditions). 

Although the preceding remarks apply pri- 
marily to developmental work, they have an 
important bearing on the evaluation of produc- 
tion fuzes. In examining the data on field per- 
formance, the following characteristics will 
frequently be noted. 1. The data are volumi- 
nous for acceptance test conditions but, for 
many fuzes, quite scanty for other conditions 
(e.g., other projectiles or velocities). 2. There 
is frequent evidence of statistically significant 
but unexplained variations between results 
supposedly obtained under the same conditions 
or between observed and predicted perform- 
ance. 

Although a very large amount of field test- 
ing was done, it was impossible, under the con- 
ditions that existed, to test all fuzes under all 
important conditions. The available facilities 
had to be reserved for the most urgent prob- 
lems. The value of engineering predictions 
based largely on laboratory data, as attested by 


the development work, and by the performance 
of the fuzes that were tested under a variety of 
conditions, provides a reasonable assurance 
that certain gaps in the pattern of field data 
need not cause great concern. 

With regard to the statistically significant 
variations, it will be noted that they are in most 
cases too small to be of practical importance in 
the military use of the fuze. In some cases, 
explanations might be given in terms of the 
approximations involved in the theory, labora- 
tory, or field testing of the fuzes. These expla- 
nations are usually mentioned only in those 
instances where the discrepancies are consid- 
ered to be of a practical magnitude. 


915 Terminology 

Fuze Nomenclature 

In presenting the results of acceptance test- 
ing, the designations of Chapter 5 are used. 
The results of tests performed under other con- 
ditions were obtained in many cases with both 
production and pilot-production fuzes (see Sec- 
tion 9.1.2, class 3) . Where a mixture occurs, the 
simplest Army Ordnance designation is used 
(e.g., T-51 for T-51, T-51-E1, T-51-E2, or 
M-166). The exact composition of the group 
is determinable through the reference system 
for tests. 

Manufacturers’ names are used to some ex- 
tent on account of certain differences in per- 
formance of the same fuze produced by differ- 
ent manufacturers. Almost all of the important 
differences in general quality of performance 
were associated with fuze design rather than 
with manufacturer. However, in the study of 
the effect of certain factors on fuze perform- 
ance, e.g., effect of altitude of bomb release 
on burst height, it is sometimes necessary to 
distinguish between manufacturers in order to 
obtain a strictly valid test of the particular 
factor under consideration. 

For the sake of simplicity, certain obvious 
abbreviations are used for manufacturers’ 
names. 

Type of Function 

The most important terms and abbreviations 


sec: 


FUZES FOR 4.5-IN. ARMY ROCKETS 


363 


are given in Chapter 5. Additional terms and 
comments on usage in the older literature ap- 
pear in the appropriate sections of this chapter. 

Errors 

Values given for the mean distance to a burst 
are calculated where possible from photo- 
graphic data obtained by methods described in 
Chapter 8. Only where photographic data were 
not available are visual estimates used. Only 
in acceptance testing is a large quantity of vis- 
ual data (camera obscura method) involved. 
The discussion of systematic observational er- 
rors is covered in Chapter 8. The values of 
standard deviation of a distribution and stand- 
ard error of the mean that are given in Chap- 
ter 9 are calculated from individual observa- 
tions of the test (or tests) involved. Except 
where stated, no attempt is made to allow for 
sources of systematic errors. In most cases 
these measures of precision are utilized only in 
the comparison of mean values obtained under 
like observational conditions, so that the sys- 
tematic component of error is balanced out. 

Methods used in estimating the probability 
of fortuitous differences are those available in 
standard modern texts. 98 


92 FUZES FOR 4.5-IN. ARMY ROCKETS 

921 Introduction 

This chapter section deals with the perform- 
ance of T-5 and T-6 fuzes for the Army 4.5-in. 
rocket. 

There was a large amount of testing that 
provided information on the performance of 
both the T-5 and the T-6 fuzes. For this reason, 
the discussion of the performance of the two 
fuzes is preceded by a section on tests that pro- 
vided basic information on the performance of 
both fuzes. 

It should be noted that in target firing at 
Corncake (Fort Fisher, N. C.) Proving Ground 
(700 ft from launcher to target) 0.4-sec 
SW-200 switches were used, while at Blossom 
Point (1,200 ft from launcher to target) 0.7- 
sec SW-200 switches were used. 

The following terminology is used in this 


chapter. In firing from the ground, or from 
a plane, for function on approach to a ground 
or water surface : 

E = Early function, a function within 5 sec 
of firing in the absence of any legitimate target. 

M — Middle, or mid-flight function, a func- 
tion that occurs more than 5 sec after firing but 
too soon to be regarded as a proper function on 
approach to the ground or water surface. 

P = Proper function, a function that occurs 
on approach to the ground or water surface 
within limits of height that experience has 
shown to be reasonable for normal operation of 
the fuze. The term Pw or Pg may be used to 
indicate that the function occurred over water 
or over ground, respectively. 

D = Dud. 

N = Number of fuzes fired. 

For the benefit of anyone who has occasion 
to refer to source material, it should be noted 
that at times the following terminology has 
been used: W for Pw; A (approach) for P. In 
firing at short range at a mock target (as in 
acceptance testing), the following terms have 
meanings different from those defined above. 

E = Early function, any function occurring 
before the target at a distance so great that a 
proper function would be highly improbable. 

P — Proper function, a function that occurs 
at a position such that, judging from experi- 
ence, it may reasonably be attributed to normal 
interaction between the fuze and the target. 

L = Late function, a function that occurs 
after the region of P’s. 

I = Impact function, one that occurs on strik- 
ing the surface. In the source material and 
reports on target tests, the term T (target) 
has been used extensively for P. Also, L has 
been used for spontaneous late functions, with 
functions attributed to the passage over a land- 
water boundary or to approach to water classi- 
fied as B or W, respectively. In most cases the 
number of functions in these classes was so 
small that subdivision of the L class appears 
unwarranted for the present purpose. 

Although scores and scoring methods can be 
discussed best in connection with experimental 
results, a few preliminary remarks are desir- 
able for purposes of orientation. Proper func- 
tion scores are in all cases given as the number 


5ECRET 


* 


364 


ANALYSIS OF PERFORMANCE 


of proper functions expressed as per cent of 
the total number of fuzes fired, excluding from 
consideration those rounds that did not have a 
fair chance, e.g., rocket blowups or rounds that 
passed outside of the region of action of a 
target. 

Early function scores may be reckoned in 
different ways. For example, in the extensive 
special studies on the causes of early function- 
ing, duds provided no information, and it was 
customary to exclude them from consideration 
in calculating the early function percentage. 
Fuzes that had functioned early could not again 
function in mid-flight, so it was customary to 
express the middle function score as a percent- 
age of middles plus propers, usually excluding 
duds as in calculating the early function score. 

These scoring methods, which were suitable 
for basic studies, are not directly interpretable 
into performance of T-5 and T-6 fuzes. The 
interpretation will be discussed after the data 
have been presented. At this point it is merely 
noted that a middle function would probably 
appear as a proper function in the T-5 appli- 
cation (provided the rocket passed reasonably 
close to a target). Further, since no correla- 
tion was found between middle and early func- 
tioning and since early functioning does not 
occur in the T-6 because of reliability of the 
arming mechanism, the early functions may be 
disregarded in estimating the performance of 
T-6 from many tests in which the SW-200 
switches were used. 


92 2 Tests Yielding Basic Information 
on Both Types of Fuzes 

Early and Mid-Flight Functioning 

On the basis of the principal causes of mal- 
functioning of the T-5 and T-6, the random 
functions have been divided into two classes, 
early and middle, as defined in the preceding 
section. 3 * 5 * 17 ’ 32 Although the line of demarca- 
tion (5 sec) is somewhat arbitrary, it will be 
seen from the following discussions of the two 
types of functions that from a practical stand- 
point this division is quite satisfactory. 

Early Functioning (Afterburning). On 
many rockets a radio proximity fuze is handi- 


capped by malfunctioning which is due to aft- 
erburning of the rocket propellant (cf. Section 
2.13). When flame issuing from the rocket 
nozzle is ionized, it increases the effective 
length of the rocket as an antenna, and makes 
a change in the radiation impedance. Sudden 
changes in the length of the flame make rapid 
changes in the radiation impedance and hence 
produce the same effect on the fuze as the 
normal target. For this reason fuzes are gen- 
erally constructed so that arming is not com- 
pleted until after the primary burning flames 
from the rocket have ceased. Frequently, how- 
ever, there is a burning following the primary 
burning, known as afterburning, and it is well 
established that this afterburning is one of the 
major causes of malfunctioning of rocket 
fuzes. Static experiments were performed to 
establish the correspondence of the fuze per- 
formance with the properties of these after- 
burning flames. These experiments also showed 
that flame sometimes was present without 
pulses but that triggering pulses were not pres- 
ent without flame. Therefore, in order to avoid 
an excessive proportion of malfunctions, it is 
desirable to eliminate or control afterburning 
from the motor. b 

For the best performance of the rocket, the 
pressure within the motor should decrease only 
slightly during the primary burning. The pres- 
sure within the motor, however, is strongly 
dependent upon the surface area of the propel- 
lant which is burning, so that after the surface 
has decreased by a small amount, the pressure 
has decreased by a larger amount. In order to 
maintain the pressure, the shape of the pro- 
pellant used in rocket motors is such that its 
burning surface remains nearly constant 
throughout the primary burning. In the 4.5-in. 
Army rockets, which use solvent-extruded Bal- 
listite, the grains of propellant are tubular and 
the burning proceeds both from the outside of 
these tubes and from the inside at the same 
time. The surface on the outside of the grains 
decreases and the surface on the inside of the 
grains increases at essentially the same rate, 

b Early attempts to eliminate malfunctioning during 
the secondary burning period took several different 
forms. Plugs to close the nozzle after the main blast, or 
“sweeps” to remove residual powder, were tried. None 
of these methods gave satisfactory results. 


SECRET 


FUZES FOR 4.5-IN. ARMY ROCKETS 


365 


so that the total surface remains nearly con- 
stant, except for the shortening of the length 
of the grains. 

When burning has proceeded until the web 
of Ballistite has been burned through over a 
considerable portion of the grain, the surface, 
and therefore the pressure, is reduced to such 
an extent that primary burning is no longer 
supported. In the Army 4.5-in. rocket the pri- 
mary burning stops at about 0.2 sec. At this 
instant, the temperature of the remaining Bal- 
listite is very little greater than it was before 
the primary burning started, because the sur- 
face of the Ballistite, which was receiving heat, 
was being consumed rapidly. After the primary 
burning has stopped, and Ballistite is not being 
consumed rapidly, the residue of Ballistite is 
heated by radiation from hot metal parts with- 
in the motor. A secondary low-pressure burn- 
ing begins then and continues until all the re- 
maining Ballistite is either consumed or 
ejected. 0 This seldom lasts more than 4 sec. 

The products of combustion of the Ballistite 
during the primary burning consist of some 
inert gases such as C0 2 and N 2 and also some 
incompletely burned products such as CO and 
H 2 . The incompletely burned gases, when mixed 
with the oxygen of the air outside the rocket, 
are probably the cause of the luminous flame 
during the primary burning. During the sec- 
ondary burning, there is probably an even 
greater proportion of flammable gases which 
can combine with the oxygen of the air to pro- 
duce luminous flame. It seems to be a matter of 
chance, however, whether these flammable 
gases on issuing from the rocket nozzles will 
ignite or not. The constituents of the Ballistite 
also determine, to some extent, whether these 
gases ignite or not ; for example, Ballistite 
salted with 1.5 per cent K 2 S0 4 has much less 
afterburning than the unsalted Ballistite. The 
expansion ratio in the rocket nozzles may also 
have a determining effect upon the temperature 
and consequent ignition of these gases. 

Since it was recognized that the burning of 
the residual Ballistite was causing malfunc- 
tioning of the fuzes, some method was sought 

c Insulation of various sorts was applied to trap wires 
and inside of motor but no improvement in performance 
was noted. 


to consume this Ballistite before the fuzes 
armed. It was suggested that a mixture of 
nitrate and picrate salts could be found which, 
when mixed with a suitable binder and pressed 
into pellets, would burn for 0.5 sec. Such pel- 
lets, when added to the propellant charge, were 
expected to consume the slivers of Ballistite 
and entirely eliminate all flammable material 
from the motor chamber before the arming 
time of the fuze. Section H of Division 3 of 
NDRC in Washington, and Division 8 of 
NDRC at Bruceton, Pennsylvania, cooperated 
in this search and developed “maintainer pel- 
lets, ” or “purge pellets” (as they were com- 
monly called), for this purpose. 

Tests had shown that when normal Ballistite 
was used, nearly 70 per cent of the fuzes func- 
tioned before 5 sec. Such functions were called 
early functions. The addition of certain pellets 
reduced the number of early functions to less 
than 20 per cent. Contrary to expectations, 
however, afterburning was not completely 
eliminated. Firings at night showed that after- 
burning often persisted continuously for an 
even greater time when pellets were used than 
when the standard charges were used, although 
the afterburning was not so brilliant as it often 
was without pellets. It is possible that the effec- 
tiveness of the pellets was due in part to the 
greater steadiness of the afterburning and in 
part to its reduction. 

At about this time, during the development 
of these pellets, a variation in performance of 
the rounds without the pellets was noticed 
which was at first attributed to the particular 
lot of propellant which happened to be loaded 
in the motors. It was proven later, however, 
that the lot of propellant had little, if anything, 
to do with the fuze performance, but that the 
variations in performance were almost en- 
tirely dependent upon the interior metal parts 
of the rocket motor. It was found, for example, 
that the M-9A1 rocket motor gave about half 
the percentage of early functions which the 
earlier M-9 motor had given and the M-9A2 
motor gave an intermediate performance. 

The most striking discovery was that with 
a double supporting ring at the base of the 
trap on which the propellant was loaded there 
were about 67 per cent early functions, where- 


SECRET 


366 


ANALYSIS OF PERFORMANCE 


as with a single supporting ring at the base of 
the trap there were only about 25 per cent early 
functions. Later a scalloped ring at the base 
of the trap was developed by the Army as a 
standard for this rocket, and with it there were 
only about 18 per cent early functions. The 
early functioning on the rockets was reduced 
by this trap to about the same extent as by the 
pellets on the double-ring traps. 

Subsequent experiments were made, using 
single-wire traps of different weights, and using 
varying amounts of metal near the nozzle end 
of the motor, but no explanation of the marked 
effect of traps has yet been found. Furthermore, 
extensive measurements of nozzle sizes, ratio 
of length to throat diameter, were made when 
the performance of later models of the M-9- 
type, with variations in nozzle dimensions, were 
found to give improved performance. These, 
however, shed no light on the problem. 

Simultaneously with the development of pel- 
lets, work was done on salted powders. Some 
of the more successful ones reduced the per- 


Table 1. Early function! scores* for T-5 fuzes 
on 4.5-in. Army rockets. Elevation is 60° or 
greater unless otherwise noted. 


Trap ring 

Motor 

E 

M 

Pw 

%Et 


Load: regular double-base propellant 



Single wire 

M-9 

33 

12 

85 

25 

12 

Single wire 

M-9A1 

4 

9 

34 

9 

21 

Double wire§ 

M-9 

443 

45 

175 

67 

20 

Double wire 

M-9A1 

35 

6 

55 

36 

10 

Scalloped 

M-9 

22 

13 

90 

18 

13 

Scalloped 

M-9A1 

11 

28 

107 

8 

21 

Load: regular plus 10 pellets 





Double wire 

M-9 

23 

30 

104 

15 

22 

Load: salted powder 






Double wire 

M-9 

17 

12 

57 

20 

17 


* Note: The better scores on the M-9A1 motors may be attribut- 
able to the rotation of this projectile, which is brought about by 
hand crimping of the fins. 

t Including middle-function performance; see following section for 
discussion of middle functioning. 

t Disregarding duds, i.e., 100 E/(E + M + Pw ) . 

§ 58 of these were at 45° quadrant elevation, 27 E, 3 M, 28 W. 

centage of early functions, with double-ring 
traps, to about 20 per cent. When a mixed load, 
part salted and part unsalted, was used, inter- 
mediate scores were obtained. 

It should be mentioned that investigations 
were made of the effect of powder weight, of 
motor velocity, and of the dampness and tem- 


perature of propellant. In certain cases some 
change in the time distribution of earlies was 
noted, but there was no appreciable dependence 
of functioning scores on any of these factors. 

In Table 1 scores for various motor, trap, 
and propellant combinations are given. Time 
distribution of earlies is shown in Figure 2. 



T-5 fuzes (high-angle firing) : A, with double- 
wire ring at rear of trap; B, with single-wire 
ring at rear of trap ; C, with purge pellets. 

Middle Functioning. The principal known 
cause of the random functions with T-5 and T-6 
fuzes classified as middle (after 5 sec) is faulty 
fin assemblies. Rounds fired, at 30-degree ele- 
vation, on 4.5-in. rockets with nonlocking fins 
give approximately 70 per cent such malfunc- 
tioning. By proper modifications (crimping) to 
insure locking of the fins in the open position, 
this percentage may be reduced to about 20 or 
less. Such expedients as brazing and welding 
the fins in the open position also lowered the 
middle-function score, in some cases quite mark- 
edly. However, since rigid fins prohibit the use 
of a smooth-bore tube as a launcher, emphasis 
was not placed on their development. 

Following the discovery of the strong depend- 
ence of early functioning on the type of trap 
used, a comprehensive study was made of ex- 
isting results to determine any relation that 
might exist between middle functioning and 
known variables (other than fin assemblies) 
such as motor traps and propellants. No de- 
pendence of middles could be found upon (1) 
trap construction, (2) type of propellant, in- 
cluding pellets and salted powders, or (3) fre- 
quency band of the fuze (i.e., Red, Yellow, or 


SECR 


FUZES FOR 4.5-IN. ARMY ROCKETS 


367 


Green). Here it should be mentioned that ex- 
periments were performed to test the effect 
upon fuze performance of loose joints, both 
between shell and fuze and shell and motor. It 
was shown that any reasonable looseness of 
these joints would not produce an increase in 
middle functioning. 

When results were sorted according to manu- 
facturer, however, statistically significant dif- 
ferences were found as follows : 


The possibility of such functioning was in- 
vestigated in a test where 60 T-5’s, mounted on 
HE-loaded 4.5-in. rockets, were fired in 12 sal- 
vos of 5 each. The nominal time interval be- 
tween successive rounds was 0.1 sec. The 
launchers, 10 ft long, were mounted in parallel 
with a space of 10 in. between centers and at 
an elevation of 50 degrees. The self-destruction 
[SD] switch of one fuze in each salvo, usually 
that in the middle position, was set to go at 


Mfr. 


Overall 
% middle 


% middle in 
30 sec* 


No. of rounds 
on which % 
is based 


A 

14.3 

12.1 

B 

29.1 

24.6 

C 

26.0 

22.0 


938 

598 

78 


* Thirty seconds is approximately the flight time for maximum 
firing elevation (42 degrees) prescribed by the Army. 


Plots of “per cent still good” versus time, 
were made and found to take the form of ex- 
ponential curves. When these curves were ex- 
trapolated back into the early-function period, 
it was found that from 5 to 10 per cent of the 
malfunctions scored as earlies should probably 
be attributed to the middle-function phenom- 
enon. 

A very satisfactory reduction of middle func- 
tions was found in units which had survived 
rather violent “shaker” testing in the labora- 
tory (see Section 7.4). Forty-one units not sub- 
jected to such testing gave 22 per cent middles, 
while 27 shaker-tested units fired under similar 
conditions gave no mid-functions. 

A summary of representative middle-func- 
tion performance is given in Table 2. Figure 3 
shows the time distribution of middle functions 
for some 64 rounds on Revere M-9 4.5-in. rock- 
ets with nonlocking fins (30-degrees quadrant 
elevation [QE] ) . This distribution, which 
shows no particular bunching of functions at 
any specific time interval, is typical of the T-6 
middle-function performance. 

Mutual Interference 6 

So far the discussion of random functions 
has been confined to rounds fired singly. It is 
evident that in multiple firing a serious prob- 
lem might arise from sympathetic functioning, 
i.e., the triggering of one fuze by the function- 
ing of a neighboring fuze. 


Table 2. Middle-function scores for T-5 and T-6 
fuzes on 4.5-in. Army rockets. 


Fin type 

Per 

cent 

middle* 

Quad- 

rant 

No. of eleva- 
rounds tion 
mid and (in 

proper degrees) 

Fuze 

mfr. 

T-6 

Locking, factory 
crimped 

19 

91 

25-40 

B 

Nonlocking 

69 

106 

30 

A, B 

Hand crimped 
(locking) 

21 

85 

30 

B 

Hand crimped 
(locking) 

15 

59 

70 

A 

Crimped and 
brazed 

23 

47 

70 

A(T-5) 

Welded, single 
thickness 

10 

49 

30 

B 

Welded, double 
thickness 

7 

14 

40 

A 

Welded, double 
thickness 

28 

32 

60 

A 

T-5, shaker tested 
Hand crimped 

4 

45 

45 

D 

Hand crimped 

0 

27 

70 

D 

T-5, controls for shaker tested 

Hand crimped 22 41 

70 

D 


* %M = 100 M/(M + W). 


2.5 sec, so that one fuze would be certain to 
function before the normal time for SD func- 
tioning (usually between 6 and 12 sec). d 

Results of the test were somewhat compli- 
cated by several factors. 

1. Not more than half the fuzes set for an 
early SD time functioned during the desired 
period. (This meant that only a very small 
amount of data covering the useful portion of 
the T-5 flight could be obtained.) 

d T-5 fuzes normally come equipped with this type of 
switch although discussions in previous sections pertain- 
ing to middle functioning of the T-5 fuzes were confined 
to results with fuzes in which the SD switch had been 
shorted out. 


▼secret 


368 


ANALYSIS OF PERFORMANCE 


2. Variations in initial velocities and irreg- 
ularities in firing intervals made distances be- 
tween rockets in flight quite uncertain. 

3. Times to function as determined by stop- 
watch could not be considered very accurate. 

In order to make allowance for errors in 
timing and to provide some means of analyzing 


the arming switch. In most cases the rotation 
of the projectiles was brought about by the 
deformation of fins during the crimping proc- 
ess. A series of field tests confirmed laboratory 
results on the delay or prevention of arming 7 ’ 16 
due to rotation. A general conclusion was that 
the effect became serious if the fins were tilted 



Figure 3. Distribution of functions in mid-flight, T-6 on M-9 with nonlocking fins. Elevation: 30°. 
Eash dash on trajectory shows approximate position of a function. 


the data, the following method was used. To 
each round there was assigned a 0.4-sec inter- 
val spanning the given time to function. A rea- 
sonable measure then of the presence of sympa- 
thetic functioning was a comparison of the 
number of overlapping intervals within salvos 
and those between salvos. 

Statistical analysis showed good agreement 
between expected (fortuitous) and observed 
members of overlapping pairs within and be- 
tween salvos. This indicated that no appreci- 
able sympathetic functioning occurred. 

Miscellaneous 

Spin Effect on Arming. The SW-230-type 
arming switch, when used on nonrotating pro- 
jectiles, is very reliable. When, however, this 
switch is subjected to rotation in excess of a 
certain minimum speed, faulty performance is 
to be expected. Laboratory testing has shown 
that for rotational speeds up to 600 rpm normal 
functioning occurs; above 900 rpm, the switch 
does not arm at all ; and between these two ex- 
tremes there is an increasing time required to 
complete arming. 13 The effect was of practical 
importance because a slight twist on the fins 
of an M-8 rocket might produce enough rota- 
tion to interfere with the proper operation of 


more than 2 degrees from their proper position. 

Rain Effect. The T-5 (or T-6) fuze when 
fired in moderate or heavy rain cannot be de- 
pended upon to ride through to proper func- 
tion. The triggering pulses from impact with 
the drops can be significantly reduced, however, 
by the use of Lucite caps cemented over the 
conical surface of the fuze. The following gives 
a comparison of function scores for rounds 
fired during rainfalls of comparable intensity 0 
with and without such “rain caps.” 

E M Pw D 
With Lucite caps 10 8 1 

Without caps 5 13 2 


Photographic measurements of function 
heights indicated no appreciable effect on sen- 
sitivity from the Lucite caps. 


923 Performance of T-5 Fuzes 

Safety and Arming 

General Considerations. The arming switch 
of the T-5 is so designed that arming occurs 


e Data on frequency and size of drops were obtained 
by exposing pieces of specially prepared cloth to the 
rain for measured intervals of time. Where water hits 
this cloth a permanent colored spot is produced. 9 


SECR 


FUZES FOR 4.5-IN. ARMY ROCKETS 


369 


at a definite time after the end of burning. The 
distance from the launching point to the point 
of arming is therefore obtainable by adding to 
the burning distance the product: (mean veloc- 
ity during switch operation) X (time of switch 
operation). As the temperature of the rocket 
propellant is increased, the burning distance 
decreases and the peak velocity increases. The 
arming distance of the fuze is therefore a func- 
tion of temperature. 

When the rocket is launched from a plane, 
the distance that is of interest is the distance 
from plane to rocket at the time of arming. In 
general this distance will be less than the dis- 
tance determined in a ground launching test at 
the same temperature. This decrease in distance 
is due to the greater air drag on the rocket, 
which travels at a higher speed when launched 
from a plane. This statement is true in cases 
of firing at moderate altitudes. In case of firing 
at high altitudes, there may be a compensating 
effect due to the higher efficiency of rockets in 
rarefied atmosphere. The arming distance of 
the T-5 is therefore a function of the tempera- 
ture of the rocket propellant, the speed of the 
launching plane, and its altitude. 

Sufficient data are not available for exact 
estimation of the effects of these factors on 
arming distance. Approximate calculations in- 
dicate that the effects can be neglected, for 
practical purposes, under a fairly wide variety 
of conditions. The possibility that they might 
be of importance under extreme conditions 
should not be disregarded. 

Switch Reliability. 1. Failure to arm. Spe- 
cific data on failure to arm, as such, are not 
available. However, dud scores in acceptance 
testing establish a reliable measure of the upper 
limit of SW-200 switch failure. The overall dud 
score for 4,334 rounds was 3.6 per cent. It is 
reasonable to assume, therefore, that something 
less than this percentage of switches failed to 
arm. 

2. Safety and lower limit for arming. Data 
on time and distance to arming from direct 
measurements on units set to function on arm- 
ing with 0.7-sec switches, are very scanty. 
Again, reference may be made to acceptance 
results to establish lower limits. In Figure 4 
is given the distribution of 226 early functions 


(Blossom Point data, all on M-9) in terms of 
distance from the launcher. From this curve 
it may be seen that less than 1 per cent of the 
fuzes had functioned at the 550-ft point and 
none at 525 ft. Although there is no certainty 
that some fuzes had not armed before the 525-ft 
mark from the standpoint of safety, it is rele- 
vant to emphasize the fact that no functions 
were observed before this point. For standard 



Figure 4. Cumulative percentage of early func- 
tions, MC-382 acceptance testing. 


test conditions (ordinary temperatures and 30 
grains of propellant) this distance of 525 ft 
corresponds to a 0.7-sec flight time. 

3. Upper limit for arming. The determina- 
tion of the time or distance at which all fuzes 
(excluding duds) will become armed is some- 
what uncertain. The situation is complicated by 
the effect of motor spin upon the action of the 
switch. See Section 9.2.2 for discussion. An 
estimate of an upper limit may be made from 
the number of live units (total minus duds) 
which functioned either early or on target in 
acceptance testing. Blossom Point data show 
that at least 98 per cent of the switches were 
closed at 1,200 ft (1.4 sec, approximately). Re- 
sults of the few arming tests, however, indicate 
that when a reasonably satisfactory fin assem- 
bly is used, the majority of the switches will be 
armed after 1 sec of flight. 11 

Risk of Premature Function. The possibility 
of the occurrence of a function before normal 


370 


ANALYSIS OF PERFORMANCE 


time for closing of the arming switch is very firing at a target about 1,000 ft out, see Section 
remote. In the assembling of hundreds of stand- 9.8 for requirements for acceptance) form the 
ard units for acceptance testing and attendant greatest mass of data available concerning per- 
experimental work, no switch was ever found formance of T-5 fuzes under fairly uniform fir- 
to be in the armed position. Also in firing tests ing conditions. Although there were some differ- 
no premature functions were ever observed on ences in conditions at the various proving 
HE-loaded rounds. With inert-loaded rounds grounds, the setups were essentially the same, 
using the highly sensitive spotting charges (see Details of procedure at the different locations 
Chapter 8) the safety features of the powder may be found in Chapter 8. 
train barrier do not apply. However, even in In Table 3 scores of acceptance tests are 

Table 3. Acceptance testing results for T-5 fuzes. 

Manu- 

facturer 

Proving 

ground 

Lot No. 

No. fuzes 
tested 

P 

Per cent 

E L 

D 

Emerson 

CC* 

1-8, 10, 11 

140 

78.6 

13.6 

3.6 

4.3 


BPf 

9 and 12-59 

613 

80.9 

13.1 

2.8 

3.3 


Af 

60-65, 71-97 

338 

83.4 

11.2 

1.8 

3.6 

Total 



1,091 

81.4 

12.6 

2.6 

3.5 

Friez 

CC 

1-4 

64 

75.0 

17.2 

0 

7.8 


BP 

5-12 and 15 

101 

89.1 

3.0 

1.0 

6.9 


A 

13-14, 18-261 

120 

86.7 

8.3 

5.0 

0 

Total 



285 

84.9 

8.4 

2.5 

4.2 

GE 

CC 

1-5 

70 

74.3 

17.1 

2.9 

5.7 


BP 

6-35 

347 

86.5 

10.1 

0.9 

2.6 


A 

36-52, 55, 57-78 

429 

79.5 

16.6 

1.6 

2.3 

Total 



846 

81.9 

13.9 

1.4 

2.7 

Philco 

CC 

1-11 

166 

73.5 

14.5 

3.6 

8.4 


BP 

12-58 

570 

83.5 

11.9 

0.9 

3.7 


A 

59-77, 85-94, 98, 100, 

380 

84.2 

10.5 

2.4 

2.9 



102, 104-109 






Total 



1,116 

82.3 

11.8 

1.8 

4.1 

Westinghouse 

CC 

1-8 

114 

73.7 

13.2 

7.9 

5.3 

(Mansfield) 

BP 

9-44 

458 

79.5 

15.1 

1.3 

4.1 


A 

45-61, 65, 67-77 

360 

81.1 

14.7 

1.7 

2.5 

Total 



932 

79.4 

14.7 

2.3 

3.6 

Westinghouse 

BP 

1-4 

64 

62.5 

25.0 

10.9 

1.6 

(Baltimore) 








All 



4,334 

81.2 

13.0 

2.2 

3.6 


* Comcake Proving Ground, Fort Fisher, N. C. 
t Blossom Point Proving Ground. 
t Aberdeen Proving Ground, Aberdeen, Md. 


these cases no fully verified premature func- 
tions were reported. Occasionally (actually only 
twice in many thousands of tests) observers 
claimed to see the spotting charge operate as 
the rocket left the launcher. Since visual rec- 
ognition of the spotting charge during the 
burning of the rocket propellant is extremely 
difficult, the validity of even these rare obser- 
vations is dubious. 

Performance under Acceptance 
Test Conditions 

The results of acceptance testing (horizontal 


listed according to manufacturer and proving 
ground. Detailed analysis of the results ob- 
tained at Corncake (Fort Fisher) and Blossom 
Point may be found in reference 4. Although 
these scores lead to a reasonably good estimate 
of the overall performance for T-5 fuzes fired 
under acceptance-testing conditions, two facts 
should be pointed out: (1) individual scores 
and variations therein cannot be taken at face 
value as indicating corresponding variations in 
manufacturing quality; nor (2) can exactly the 
same performance as indicated by these accept- 
ance results be expected of fuzes fired under 


SECRET 


FUZES FOR 4.5-IN. ARMY ROCKETS 


371 


conditions unlike those of acceptance work, i.e., 
high-angle, plane-to-plane. 

It has been shown earlier that such factors 
as motor type, propellant, and kind of trap may 
very markedly affect early functioning. Still 
other factors such as temperature and varying 
distances from position of arming to target 
must be taken into consideration. Since it is 
not possible to separate these effects entirely, 
lot-to-lot variation in performance must be 
viewed with caution; specifically, for example, 
the apparent improvement in scores of tests 
conducted at Blossom Point over those done at 
Corncake must not of necessity be taken as an 
indication of improved manufacture, but rather 
as the possible result of a combination of 
many factors including perhaps even unknown 
changes in test conditions. 

Entirely apart from experimental test re- 
sults, this view is amply supported by a study 
of the acceptance test performance. For exam- 
ple, Figure 5 shows that the February 1943 
early functioning performance of fuzes of all 
manufacturers was poor on Revere rockets, but 
good on Budd rockets or Revere rockets fitted 
with Budd fins. The strikingly uniform im- 
provement in the subsequent performance of 
all fuzes on Revere rockets is not accompanied 
by any similar change on the Budd or modified 
Revere rocket. No convincing explanation has 
been found for the improvement on Revere 
rockets. 

In view of the results of later experimental 
testing where attempts were made to control 
increasingly larger numbers of variables (which 
hitherto either had remained unnoticed or had 
not appeared as relevant) the performance of 
production fuzes appears to be satisfactorily 
uniform. The overall score as given in Table 3 
gives 81 per cent proper; it is safe to say that 
with a satisfactory trap-ring-motor-propellant 
combination a slightly higher score could now 
be expected. (Much of the acceptance work 
was done before high-angle testing showed the 
importance of these three factors.) 

Effect of Distance to Target 
on Performance 

Compared with those in actual combat use, 
the distances between arming and target in ac- 


ceptance testing were somewhat limited. This 
means that in actual use, then, there would be 
greater opportunity for the fuze to malfunction 
before reaching the proper destination and, if 
so, proper function scores would be lower. 

Since the period for early functioning as de- 
fined in Section 9.2.2 is about equal to the mini- 
mum time taken for the SD feature of the T-5 
to work, estimates of reliability for combat use 
(for ranges longer than the acceptance test 
range) can easily be made from results of high- 
angle testing. The early functions remain clas- 
sified as early and all other functioning rounds 
become proper (see Section 9.2.2 for repre- 
sentative scores). Figure 2, in Section 9.2.2, 



o 



Figure 5. Early function performance in ac- 
ceptance testing of MC-382 rocket: Budd or 
Revere with Budd fins (top) ; Revere, inert- 
loaded or empty head (bottom). G General 
Electric, E Emerson, F Friez, P Philco, 

W Westinghouse. 

shows time distribution of early functions for 
various types of trap. When adjustment is made 
for a 4 per cent dud score, the following per 
cents proper obtain for rounds passing within 


372 


ANALYSIS OF PERFORMANCE 


radius of action [ROA] of target for the indi- 
cated flight times. 


Flight time (sec.) 

1.0 

2.0 

3.0 
4.5 


Estimated per cent proper 
Worst trap Best trap 


85 

41 

35 

32 


91 

84 

82 

81 


These values are based on the assumption 
that performance for combat firing will be com- 
parable to high-angle results. The early func- 
tion scores in high-angle firing during the first 
1.3 sec of flight and those for target testing 
(about 1.3 sec to target) are comparable when 
allowance is made for variations in motor con- 
struction and propellant. This fact gives assur- 
ance that the above estimates are fairly reliable. 

Effect of Dispersion of Trajectories on 
the Distribution of Bursts about a Target 

Analysis by the Applied Mathematics Panel, 
NDRC, 41 of results with some thousand fuzes 
tested on the mock-plane target (% scale of 
B-25 bomber) at Blossom Point indicated, for 
firing from astern, the following dependence of 
target functioning upon distance of passage 
from target axis (impact parameter). 


Impact 

Per cent of total rounds less 
duds and earlies functioning 

parameter (ft) 

on target 

10 

100.0 

20 

99.9 

30 

99.3 

40 

95.0 

50 

79.7 

60 

50.8 

70 

21.5 

80 

5.5 

90 

0.8 

100 

0.1 


The distribution of target functions for 
rounds fired through ROA for acceptance re- 
sults is shown in Table 4. In Figure 6 are shown 
graphically the distributions for two values 
of impact parameter. For empirical equations 
to represent these distributions see reference 41. 

Effectiveness in Plane-to-Plane Firing 

A study was also made by the Applied Math- 
ematics Panel to determine the probability that 


a single 4.5-in. rocket fuzed with T-5 (when 
fired from 1,000 yd directly astern) would dis- 
able an enemy twin-engined bomber (Ju-88). 
It was assumed that the rocket trajectories 
have circular symmetry about the longitudinal 
axis of the aircraft; specific dispersion data 
used were from results at various proving 
grounds. The value of fuze reliability used was 
based on Blossom Point and Corncake data. 
Estimates of damage by a projectile were based 
on material presented in reference 40; these 
estimates considered damage not only to the 
engines but to various vulnerable portions of 
the plane. 

Calculations were made on two assumptions : 
(1) that the plane could not return to base on 
one engine, and (2) that the plane could return 
to base on one engine only. The following re- 
sults were obtained: 


Standard deviation* Probability of disabling 
of firing errors (ft) the aircraft 

Aircraft assumed unable to return on one engine 
25 0.207 

50 0.106 

75 0.057 


Aircraft assumed able to return on one engine 
25 0.143 

50 0.066 

75 0.035 


* With a 50-ft firing error (standard deviation) the chance of a 
direct hit is about one in a hundred.4i 


Effectiveness in Plane-to-Ground Firing 48 

In a test to compare the effectiveness of VT- 
fuzed and contact-fuzed rockets against person- 
nel in slit trenches, 100 rounds of 4.5-in. rockets 
(T-22, with T-23 fins), fuzed with T-5 were 
fired from a plane over the effect field (Eglin 
Field) described in Section 9.4.5. (Testing with 
contact fuzes was discontinued after 18 rounds 
fired — to ricochet — did not ricochet properly, 
and gave an excessive number of low-order func- 
tions.) Twenty each of the T-5’s were fired in 
dive angles of 10, 20, 30, 40, and 50 degrees. 

Table 5 shows the number of casualties 
(scored as in Section 9.4.5) per burst at vari- 
ous heights, for 4 degrees of shielding. 

It is important to note that the significance 
of “zero shielding/’ in this test, is somewhat 
different from that appearing in some of the 
literature on the effectiveness of air-burst pro- 


FUZES FOR 4.5-IN. ARMY ROCKETS 


373 


jectiles. In this test the vulnerable area pre- 
sented to any fragment moving in a horizontal, 
or upward direction, is zero (unless the burst 
occurs inside a trench) in the case of zero 


sented to a burst occurring in the plane con- 
taining the targets. The principal weakness of 
the latter definition arises from the fact that 
enemy troops would very rarely be distributed 


Table 4. Distribution of functions in target firing of T-5 fuzes on Revere inert-loaded motors at Blossom 
Point, March 1943 to March 1944. 


Impact Parameter p — V# 2 + z 2 (ft) 



8 

1 

3 1 

8 2 

3 2 

8 3 

3 3 

8 4 

3 4 

8 5 

3 58 

Total 

15 









2 

1 


3 

10 









1 

1 


2 

5 









1 

1 


2 

0 






1 



4 

2 


7 

—5 





4 

4 

1 


2 

2 


13 

—10 




2 

10 

8 






20 

—15 




2 

5 

10 

2 





19 

—20 



1 

6 

21 

6 

1 


1 

1 


37 

—25 



5 

52 

100 

41 

4 





202 

30 



2 

73 

180 

68 

6 


5 

1 


335 

£—35 



1 

45 

130 

72 

4 


2 

7 


261 

X 

i 

o 




2 

29 

17 

3 


9 

2 


62 

—45 





1 

1 



5 

1 


8 

—50 













—55 













—60 













—65 













—70 





1 







1 

Subtotal 



9 

182 

481 

228 

21 


32 

19 


972 

E 


2 

2 

20 

51 

16 

2 





93 

L 





2 



1 

6 



9 

D 


2 

9 

14 

3 






28 

Total 

1 2 

13 

211 

548 

247 

| 23 

1 

38 

19 

1 1,102 


Table 5. Casualties as a function of burst height. 


Burst 

height 

(ft) 

12-in. 
shielding 
(conservative) * 

Casualties 

12-in. 

shielding 

per burst 

6-in. 

shielding 

0-in. 

shielding 

0-5 

0.6 

0.8 

1.0 

1.9 

6-15 

1.8 

2.3 

3.0 

5.9 

16-30 

1.8 

3.1 

3.7 

6.6 

31-50 

2.4 

3.7 

4.3 

6.1 

51-80 

1.4 

2.2 

2.7 

3.9 

81-125 

1.2 

1.5 

2.5 

4.2 


* Counting only those bottom hits more than 6 in. from nearest edge of box (5 sq ft vulnerable area instead of 12 sq ft). 


shielding. Although this definition is not be- 
yond criticism, it is considered to be more prac- 
tical than one alternative which considers that 
the maximum possible vulnerable area is pre- 


in a mathematically plane surface. For a fuller 
discussion of this topic the reader is referred 
to Section 9.4.5. 

Figure 7 shows (1) mean burst height versus 


SECRE' 


374 


ANALYSIS OF PERFORMANCE 


dive angle, (2) casualties per burst versus dive indicate that the relative effectiveness of air 
angle, (3) casualties per burst versus burst and ground bursts is not critically dependent 
height. on the degree of shielding, and there is no rea- 



O 



Figure 6. Distribution of T-5 bursts along trajectories near fixed mock-plane target. 


In actual combat, the casualties per burst son to expect that it would depend on the con- 
would depend on the degree of concentration of centration of the enemy. 

the enemy troops and on the shielding. The data At the optimum burst height, about eight 


FUZES FOR 4.5-IN. ARMY ROCKETS 


375 


times as many casualties were obtained as with 
ground bursts. On account of scatter in the 
burst heights, and differences in the reflection 
coefficient of various terrains, the optimum 
height cannot be realized in combat. However, 
the results show a rather wide range of burst 
heights for which the relative advantage of the 




DIVE ANGLE (DEGREES) 



Code 

A 

B 

C 

D 


BURST HEIGHT (FT) 

Depth of 
shielding 
(in.) 

0 

6 

12 

12 


Vulnerable 
area 
(sq ft) 
12 
12 
12 
5 


Figure 7. Effectiveness of T-5 fuzed 4.5-in. 
rockets for various degrees of shielding — plane- 
to-ground firing: mean burst height as function 
of dive angle (top left) ; casualties as function 
of dive angle (top right) ; casualties as function 
of burst height (bottom). 


air burst over ground burst is larger and nearly 
independent of the degree of shielding. This 
useful range of burst heights is most closely 
realized by firing in the steeper dives. Again 
this is not at all critical, but dive angles in ex- 
cess of 30 degrees are indicated (cf. footnote c 
of Chapter 1). 


9,2,4 Performance of T-6 Fuzes 
Safety and Arming 

General Characteristics of Arming Switches . 
Mechanically the arming switch for the T-6 is 
the same as that for the T-5. In addition further 
delay is introduced by means of an electric 
resistance-capacitance circuit. When mechani- 
cal arming is completed, a switch is closed 
which allows current to flow from the battery 
through an arming resistor into the arming 
condenser. The voltage on the condenser rises 
until it is large enough so that a positive pulse 
into the thyratron will cause it to fire and set 
off the detonator. (There is a region of time 
just before the condenser is charged sufficiently 
to complete the arming cycle during which a 
pulse on the input to the thyratron will cause it 
to become conducting. This removes a portion 
of the charge accumulated, without firing the 
detonator. This phenomenon, called “dumping” 
(cf. Section 3.3.6), occurs only if the fuze re- 
ceives a firing signal sometime during the in- 
terval when the condenser has voltage enough to 
ignite the thyratron but does not contain 
energy enough to fire the detonator. If such an 
accidental “dumping” signal occurs, the circuit 
automatically recovers and arms at a time about 
20 per cent longer than normal. This phenom- 
enon does not cause serious trouble under ordi- 
nary circumstances. 

Arming Time and Distance. Direct measure- 
ment of arming time cannot be made for 
switches incorporating an RC delay (see Sec- 
tion 8.3.7). However, from laboratory determi- 
nations of values of the various electric com- 
ponents, along with measured times to mechan- 
ical arming, satisfactory predictions of arming 
times for the T-6 can be made. 23 ' 24 

The validity of such predictions is substanti- 
ated by field tests of Navy rocket fuzes (see 
Section 9.3.2) in which fuzes were “pulsed” 
during flight by a transmitter located on the 
firing range. Such tests do not determine the 
arming time of an individual fuze, but they do 
give an experimental lower limit on the fraction 
of fuzes fully armed at any given time. 

Figure 8 shows the per cent of fuzes armed 
as a function of time and of horizontal range 
for rounds fired on Revere 4.5-in. rocket (V 0 = 


376 


ANALYSIS OF PERFORMANCE 


840 fps). It will be seen that no fuze can func- 
tion before a horizontal range of 800 yd and 
95 per cent will be armed at 1,650 yd. (If the 
projectile passes within 150 ft of crests or other 
suitable targets before arming is complete, 
“dumping,” as mentioned above, may occur. 
Under these conditions the percentage of 



Figure 8. Cumulative per cent of T-6 fuzes 
armed as function of flight time and horizontal 
range. 

fuzes armed may be slightly reduced at ranges 
up to 2,000 yd.) 

Reliability 

No acceptance testing, as such, was done with 
the T-6 fuze. Since except for the arming switch, 
T-5 and T-6 are identical, estimates of reliabil- 
ity may be made from results of experimental 
high-angle testing of the T-5. An intensive 
study 32 of middle functions, random functions 
occurring after 5 sec, among some 1,600 rounds 
yields the following estimates of performance 
as a function of flight time. 


Flight time 

Per cent proper funct 

(sec) 

Mfr A 

Mfr B 

10 

92 

88 

15 

89 

82 

20 

87 

77 

25 

85 

74 

30 

84 

71 

35 

83 

70 

40 

82 

68 


The above percentages are based on rounds 
fired on 4.5-in. rockets with reasonably satis- 
factory fin assemblies. For discussion of the 
effect of fins on malfunctioning of the T-6, see 
Section 9.2.2. 

Effectiveness 

In tests of the relative effectiveness of 4.5-in. 
Army rockets using T-6 fuzes, PD M-4 fuzes 
set for ricochet air bursts, and PD M-4 fuzes set 
for superquick action, 260 rounds were fired 
over an effect field at Fort Bragg, North Caro- 
lina. 50 The field contained lx6-ft boards spaced 
5 yd apart, laterally and longitudinally. The 
boards were laid in shallow trenches with top 
surfaces 1 in. below ground level. On each 
round which burst on the effect field, the num- 
ber of boards hit by at least one fragment which 
penetrated at least % in. into the wood was 
counted. 

The results are given in Table 6. 


Table 6. Comparative effectiveness of T-6 fuze 
and PD M-4 fuzes set for ricochet air burst and 
for superquick action. 



Total 
No. of 
rounds 
fired 

No. of 
rounds 

on 

effect 

field 

Average 
height 
of burst 
(ft) 

Average 
No. of 
targets 
hit 
(per 
round) 

T-6 

76 

20 

60 

21.2 

PD M-4, ricochet air 

burst 

85 

10 

15 

16.8 

PD M-4, superquick 

action 

99 

20 


4.4 


These results, where heights are visual esti- 
mates, are quantitatively somewhat different 
from those obtained in T-5 testing at Eglin 
Field, where heights were photographically de- 
termined. (See Figure 7.) In the test of the T-5, 
greater effectiveness was observed at a burst 
height of 17 ft than at one of 60 ft. The Fort 
Bragg results do agree with those obtained at 
Eglin Field, however, in that they indicate a 
fourfold or fivefold advantage, over a contact 
burst, of an air burst occurring over a consid- 
erable range of heights. 


NAVY ROCKET FUZES 


377 


9 3 NAVY ROCKET FUZES 

931 General 

This section concerns the performance of the 
VT fuzes which are intended primarily for use 
on rockets as follows : 

Fuze 

Navyord. Army ord. 

designation designation Use Rockets 

Mk-172 T-2004 Plane to ground AR 5.0 

Model 0 

Mk-171 T-30 Plane to plane HVAR 

Model 0 

Throughout the section the following rocket 
designations, established by the California In- 
stitute of Technology [CIT], are used for con- 
venience. The aircraft rocket [AR] 5.0 is used 
to designate the 5.0-in. Mk-1 shell with the 
3.25-in. Mk-7 motor. The high-velocity aircraft 
rocket [HVAR] refers to the same shell, or the 
5.0-in. Mk-5 shell, used with the 5.0-in. Mk-1 
motor. Considerable testing was performed 
with the AR 3.5, denoting the 3.5-in. Mk-5 or 
Mk-3 (16 lb) shell and the 3.25-in. Mk-7 motor 
combination. 

The same scoring terminology and methods 
that are used for the Army rocket fuzes (see 
Section 9.2) are applied to the Navy rocket 
fuzes. 

The mass production model of the T-2004 fuze 
was subjected to two stages of acceptance test- 
ing. The first stage, the “metal parts” accept- 
ance test, was applied to a sample from each 
manufacturers’ lot of approximately 1,000 
“metal parts assemblies,” which constituted a 
“metal parts lot.” A spotting charge was used, 
and the rockets were not loaded with high ex- 
plosive. Following acceptance, these assemblies 
were loaded with the few additional explosive 
components necessary to make complete fuzes, 
and the lots were usually combined into much 
larger lots known as “ammunition lots.” The 
second stage was the ammunition lot acceptance 
test, applied to a sample from each ammunition 
lot, to check on the safety and reliability of the 
complete fuzes that were subsequently shipped 
to the using Services. A discussion of compo- 
sition of ammunition lots and the relation be- 
tween their performance and that of the metal 


parts lots is given in Section 9.4.3. Procedures 
for acceptance testing are outlined in an appen- 
dix to this chapter. 

The large difference in overall sensitivity 
makes it desirable to treat the T-30 and T-2004 
separately except for their arming character- 
istics. The latter are identical mechanically but 
differ in the amount of RC delay. 

The relation between early functioning and 
afterburning is discussed under the T-30, since 
the problem is of much greater importance 
with the fuze that has the greater sensitivity 
and shorter arming time. Also, the afterburn- 
ing of the HVAR is much more serious than 
that of the AR. 

Section 9.2.2 should be consulted for a dis- 
cussion of basic considerations relating to after- 
burning as well as for the background provided 
by experience with the T-5 Army rocket fuze. 
Conclusions concerning afterburning and early 
functioning of VT rocket fuzes in general are 
given at the end of Section 9.3.3, with partic- 
ular reference to the T-30 and the Navy rockets. 


932 Safety and Arming 

General 

The arming mechanism of the VT fuzes for 
Navy rockets is so designed that mechanical 
arming occurs when acceleration of the rocket 
ceases. Complete arming is delayed somewhat 
further by the use of an RC circuit. 

Mechanical arming tests should provide data 
that are in general agreement with the burning 
times and distances of the rockets. No exact 
comparison is practical, however, since burning 
does not cease abruptly, and mechanical arming 
occurs at some time during the final “tapering 
off” of the burning. 

The values of the RC arming network follow. 



R 

C 


Fuze 

(megohm) 

(mf) 

RC 

T-2004 

1.5 

1.0 

1.50 

T-30 

0.82 

0.90 

0.74 


The average RC delay should be approxi- 
mately equal to the product RC in seconds (see 
Section 3.3.6). For the sake of completeness 
tests with fuzes having other values for R and 
C are included in the following analysis. 


378 


ANALYSIS OF PERFORMANCE 


In addition to tests of arming performance, 
there are summarized the results of a safety 
test. This test, which was performed primarily 
as a check on the safety of the value adopted 
for arming distance, is of particular importance 
because it was conducted under conditions sim- 
ulating rather closely those of Service use of 
the fuzes. 

Mechanical Arming Performance 

The most accurate data on mechanical arm- 
ing performance are probably those obtained 
in the experimental tests, summarized in Table 
7, 5G in which most of the arming distances were 


The relatively large arming distance observed 
with the AR 3.5 is probably due to the lower 
efficiency of the propeller at the high speed of 
this rocket, which is about the same as the 
velocity of the HVAR. 

The best estimate of spread in mechanical 
arming distances (from Table 7) is given in 
Table 9. 

From an inspection of Table 7 it is evident 
that there is a lower temperature limit, in the 
neighborhood of —20 F, for the reliable oper- 
ation of the mechanical arming device with the 
AR 5.0. At —20 F, about half of the arming 
mechanisms failed to function. This limit arises 


Table 7. Results of experimental FOMA tests. 







SD of 



Mean powder 


Standard 

individual 

No. of 

Score 

temp 

Mean arming 

error of 

arming 

units 

FOMA-D-L 

(degrees F) 

distance (ft) 

mean (ft) 

distance (ft) 




Bowen and GE T-30 units on AR 5.0 



10 

9-1-0 

70 

461 

23 

68 

20 

10-9-1 

—20 

484 

13 

42 

10 

9-1-0 

—10 

476 

16 

49 

10 

9-1-0 

0 

465 

19 

58 

10 

10-0-0 

80 

439 

5 

16 



Philco T-200Jf units 

on AR 3.5 



16 

14-1-1 

71 

596 

10 

39 



Philco T -2004 units 

on AR 5.0 



15 

14-1-0 

90 

445* 


, . 

10 

9-1-0 

79 

415f 

13 

38 


* No photographic data of arming distances are available for this test. The average arming distance (445) was computed by assuming 
the average velocity in this test to be the same as the average velocity of similar rockets of other tests when fired under similar test con- 
ditions. The arming distance was then computed from the average speed and the observed arming time (1.086 sec). 

t This figure is based on the photographic data of only 3 units. 

determined photographically. Arming times 
(stopwatch measurements) ranged from about 
1.0 sec at the higher temperatures to 1.6 sec at 
the lowest. The distances given in Table 8, 
from ammunition lot acceptance tests, were 
calculated from stopwatch measurements of 
arming time. Making due allowance for timing 
errors, the values agree reasonably well with 
those in Table 7. 

For an analytical comparison of temperature 
effects on arming distance with temperature 
effects on burning distance, reference 37 should 
be consulted. Here it is sufficient to note from 
Table 7 that the effect of temperature on arm- 
ing distance is practically negligible through- 
out a rather wide temperature range. 



from the fact that a certain minimum accelera- 
tion is required for arming of the fuzes. Tests by 
Army Ordnance indicate an upper temperature 
limit in the neighborhood of 110 F. An upper 
limit arises from the fact that the propeller 
must make a minimum of approximately 100 
turns before acceleration falls below a certain 
value. For a complete discussion of the me- 
chanics of the arming device see Chapters 4 
and 5. 

Results of Pulsing Tests to Obtain Total 
Arming Distances of T-30 Fuzes 

Data are provided by a number of tests de- 
signed to determine the spread in arming times 
and arming distances of T-30 fuzes 31 on the 


NAVY ROCKET FUZES 


379 


AR 3.5. In these tests each fuze was “pulsed” 
by a transmitter at a certain point in its flight 
to determine whether or not it was armed. The 
experimental technique is covered in Section 8.3. 
The tests are very difficult to perform and the 
data are, therefore, rather limited. 


Table 8. Results of Philco acceptance FOMA tests 
of T-2004 fuzes on the AR 5 rocket. 


PA lot 

No. 

PA-315 

No. 

of Score 

units FOMA-D-L-I 

Powder 

tempera- 

ture 

(degrees 

F) 

Mean 

arming 

distance 

(ft) 

2 

10 

10-0-0-0 

72 ) 

458 

3 

10 

7-0-1-2 

72 \ 

4 

10 

9-0-0-1 

59 

542 

5 

10 

8-2-0-0 


453 

13 

10 

10-0-0-0 

82 

404 

3 

10 

10-0-0-0 

83 

554 

6 

8 

7-1-0-0 

83 

428 

Table 9. 

Mechanical arming spread of T-30 and 

T-2004 units on AR 5. 






Amount 



Pooled 

Amount 

beyond 

Total 


estimate 

short of 

the mean 

spread 


of 

the mean 

for 

1% to 


standard 

for 1% 

95% 

95% 


deviation 

armed 

armed 

armed 

Arming 





distance 

49 ft 

129 ft 

91 ft 

220 ft 


From such pulse test data it is possible to 
calculate a probability distribution of total arm- 
ing distances. The results are summarized in 
Table 10. No pulsing tests performed with other 
rockets yielded sufficient data for probability 
distributions. 


Table 10. Results of pulsing tests of T-30 units on 
AR 3.5, 1.15-mf firing condenser. 


Delay 

Arming time 

Arming distance 

resistor 

1% median 95% 

1% 

median 

95% 

(megohms) 

(sec) 


(ft) 


0.51 

1.09 1.36 1.58 

740 

1,060 

1,310 

0.75 ' 

1.26 1.53 1.76 

940 

1,240 

1,480 


The analytical comparison of the data of 
Table 10 with engineering prediction is too 
complex for presentation here. The difficulty of 
the tests was increased by lack of accurate bal- 
listic data for VT-fuzed rockets, and reference 
31 should be consulted for an adequate treat- 
ment of the data. Essentially, the analysis 


showed that there was satisfactory agreement 
between prediction and observation if it was 
assumed that one “dumping” cycle occurred in 
most of the fuzes before complete arming (see 
Section 3.3.6 for description of dumping). 

Calculated Percentage Points for 
Total Arming 

It is indicated in the preceding section that 
minimum safe arming distances can be pre- 
dicted from data on mechanical arming per- 
formance together with the engineering theory 
of RC arming. In order to make conservative 
predictions, it is desirable to assume that 
“dumping” does not occur. Maximum arming 
distances calculated on this basis are likely to 
be underestimates. However, since the number 
of “dumping” cycles that occur is likely to de- 
pend considerably on any condition, such as 
temperature, that affects afterburning, it ap- 
pears desirable to calculate the maximum arm- 
ing distance on the same basis as the minimum. 
Calculated values are given in Table 11 for sev- 

Table 11. Mechanical and total arming distances 

of rocket fuzes, 1.15-mf firing condenser. 


Delay resistor Arming distance (ft) 

(megohms) 1% Median 95% 


Mech. arming 

AR 3.5 
350 

600 

740 

0.51 

740 

1,060 

1,300 

0.75 

930 

1,240 

1,480 

1.50 

1,460 

1,760 

1,980 

Mech. arming 

AR 5.0 
330 

460 

550 

0.51 

450 

790 

1,020 

0.75 

650 

970 

1,200 

1.50 

1,180 

1,470 

1,700 

Mech. arming 

HVAR 

420 

650 

810 

0.51 

940 

1,140 

1,530 

0.75 

1,160 

1,360 

1,760 

1.50 

1,830 

2,080 

2,630 


eral values of arming delay resistance. Rocket 
ballistic tables 38 were used in making estimates 
for the HVAR. Table 11 is probably most re- 
liable when used in connection with the T-2004, 
in which “dumping” is less likely to occur. In 
connection with the T-30, especially on the 
HVAR, it should be remembered that the actual 
maximum (or 95 per cent) arming distance is 
likely to be in excess of tabulated values, on 
account of the “dumping” phenomenon. 


SECRET 


380 


ANALYSIS OF PERFORMANCE 


Tests of Safety 

Safety tests were conducted by the Navy Bu- 
reau of Ordnance at Inyokern 42 ’ 43 to determine 
the fragmentation effect, in cases of early func- 
tioning. In these tests a TDR drone was modi- 
fied to fire HE-loaded AR 5’s, fuzed with T-30 
or T-2004 fuzes, wired to fire on mechanical 
arming. The rockets were fired from under the 
wings of the drone, when the aircraft reached 
maximum airspeed in a maximum dive angle 
of about 10 degrees. The results of 27 rounds, 
all of which functioned on mechanical arming, 
showed no hits on the drone. Since these fuzes 
had no normal RC delay, it was concluded that 
rearward fragmentation damage to the firing 
plane was a very remote possibility. 

Performance of T-30 Fuzes 

Practically all the data on T-30 performance 
were obtained with pilot production models. 
Some of the early testing was done with modi- 
fied bomb fuzes. Two peak amplification fre- 
quencies, approximately 100 and 70 c, were 
tried during pilot production, and there were 
a number of other variations, including changes 
in RC delay resistor, generator shaft couplings, 
and thrust bearings. 

Because of difficulties with dispersion in fir- 
ing the Navy rockets from a fixed launcher at 
a mock-plane target (see Chapter 8) most of 
the testing was performed by firing at high 
angle or from a plane for function on approach 
to water. The relation between the scores ob- 
tained in the two types of tests has already 
been discussed in Section 9.2. 

Afterburning and Early Functioning 17 

General. Before discussing the performance 
of the T-30 in the conventional types of tests 
just mentioned, it is desirable to give some at- 
tention to the problem of early functioning and 
afterburning. A VT fuze on Navy rockets has 
to be armed at some time subsequent to the 
main burning time to avoid malfunctioning due 
to afterburning. This fact puts a serious limi- 
tation on the tactical effectiveness of the VT 
fuze on these vehicles. 

Experience with the T-5 Army rocket fuze 


had shown the importance of afterburning (see 
Section 9.2). In field tests of developmental 
models of T-30 on Navy rockets it was noted 
that there was a great deal of afterburning 
from the motors, and the poor performance of 
the fuzes was attributed to this afterburning. 
These early fuzes had no RC arming delay. 

A cooperative investigation between the 
Navy, Division 3 and Division 4, NDRC, was 
started at the Naval Ordnance Test Station 
[NOTS], Inyokern, in order to find means for 
reducing the effects of afterburning on HVAR. 

The Propellant Grain and Its Burning Char- 
acteristics. The cruciform grain of Ballistite 
used in the HVAR has a length of 39.5 in. and 
an outside diameter of 4.20 to 4.26 in. After 
ignition the burning is maintained at nearly 
constant rate by means of inhibitors. The burn- 
ing progresses until the surface of the grain 
has decreased so greatly that the resulting pres- 
sure will not support the primary burning. A 
core of unburned Ballistite remains at the end 
of the main burning. After the main burning, 
the core continues to receive heat from the 
motor wall and nozzles; its temperature is 
raised, and secondary burning is initiated. The 
secondary burning continues until the core is 
either consumed or becomes small enough to be 
ejected through the nozzle. 

The rate of secondary burning is so low that 
negligible contribution is made to the forward 
thrust of the rocket. The core is, therefore, use- 
less to the rocket and far more useless to the 
fuze, since afterburning causes malfunctions. 

Static Tests in an Air stream. Static tests at 
Alleghany Ballistics Laboratory and at Inyo- 
kern, conducted by placing the rocket in a 
stream of air to simulate some of the conditions 
of flight, showed definite correlation of fuze 
pulses with afterburning. Afterburning of the 
Ballistite caused pulses which were several 
times as strong as the pulses necessary to 
trigger the fuzes. 

Since afterburning depends on the presence 
of the core, it was decided to eliminate a large 
portion of the core by extruding the Ballistite 
grain with an axial perforation. The presence 
of the perforation suggested the possibility of 
filling the void with some substance which 
might be beneficial in overcoming the after- 


SECRET 


I 


NAVY ROCKET FUZES 


381 


burning. Sand, table salt, hypo, sal soda, borax, 
alum, and Epsom salts were tried. Empty per- 
forations were also tried. Comparisons of these 
loadings were made with standard grains. 
Hypo, alum, and Epsom salts proved to be the 
best. The others were less effective but superior 
to standard grains. It may be that evaporation 
of water of crystallization in some of these ma- 
terials might cool the gases to such an extent 
that afterburning would not be started. It was 
found to be equally effective to place quarter- 
pound bags of hypo, wrapped in cloth, ahead of 
the igniter. As a practical measure, hypo may 
be unsatisfactory, because it melts at 120 F 
(this temperature could be easily exceeded in 
motors exposed to summer sun), and even if it 
did not melt, the crystals would yield water 
vapor, which would be absorbed by the Bal- 
listite, where it might cause trouble. For these 
reasons, alum or Epsom salts would be better, 
because each of these contains as much or more 
water of crystallization and yet has a lower 
partial pressure of water vapor. Common salt 
and sand, which have no water of crystalliza- 
tion, give much better results than standard 
rounds, but inferior to those containing water 
of crystallization. The fact that hypo, alum, and 
Epsom salts, which gave the best performance, 
are sulfates suggests that the presence of sul- 
fur may be an important factor. 

Results with hypo showed no afterburn- * 
ing and no pulses in any of 13 static experi- 
ments. 

Ground-Launched HVAR Tests. The fuze had 
performed well on the HVAR, fired statically 
in the airstream, with hypo in the perforation 
in the grain. However, when such rounds were 
fired from a ground launcher, the addition of 
hypo bags impaired significantly fuze perform- 
ance in flight. The fact that hypo bags had 
eliminated the afterburning in the static tests, 
yet increased the early functioning in the flight 
tests, is one of the paradoxes in the afterburn- 
ing program. 

The HVAR rockets, modified to have single 
nozzles in place of standard multiple nozzles, 
were fired but failed to indicate a significant 
difference in performance from standard 
HVAR. It was thought that the single nozzle 
would permit ejection of the core at the end of 


primary burning, as is often observed to be 
true of AR rockets. 

Plane Firing with HVAR. The final appraisal 
of T-30 performance must come from plane 
launchings, since this type of testing is nearest 
to tactical conditions. Fuzes must be ready to 
function after the rocket is at a short yet safe 
distance from the firing plane. Effectiveness 
will be limited by the proportion of duds and 
random functions, the lateness of arming, and 
rocket dispersion. 

The results from rounds fired from a plane in 
a dive at various ranges indicated an average 
time delay of 0.3 sec due to dumping of the 
firing condenser caused by afterburning. This 
extra time is much shorter than was expected 
from the static firings and shows that static 
firings cannot be relied upon to indicate the 
performance of plane-fired rounds. 

The variation in fuze performance under 
different test conditions is further accentuated 
by comparing early-function scores of ground- 
launched and plane-launched rounds. A test at 
Inyokern of T-30 on standard HVAR, fired at 
a slant range of 2,500 yd from a plane in a 30- 
degree dive flying at 200 mph, yielded 5 duds, 
58 propers, and 27 earlies (32 per cent early- 
function score). The early functions centered 
at 1.85 sec, which is only slightly greater than 
the arming time. These results may be com- 
pared with the data in Table 12 for ground- 
launched HVAR, which show a 17 per cent 
early function score. 

Conclusions. The main conclusions obtained 
from the study of malfunctioning of VT fuzes 
and afterburning of rocket motors are as fol- 
lows: Many correlations have been made of 
afterburning and VT fuze malfunctioning, but 
as yet very little has been definitely proved 
about the fundamental causes of afterburning. 
Static experiments, using a 110-fps airstream 
past the rocket nozzle, correlate the afterburn- 
ing with pulses on the fuzes and indicate that 
a large portion of malfunctioning on the HVAR 
would be due to afterburning. Hypo, which de- 
creased the afterburning in static firings, 
caused an increase of early functions on 
ground-launched rounds. On the other hand, 
standard HVAR rockets launched from a plane 
produced a larger proportion of early func- 


SECRET 


382 


ANALYSIS OF PERFORMANCE 


tions. This suggests a real difference in per- 
formance, but it is difficult to explain why an 
increase in the airspeed of a rocket from a 
supersonic velocity to a higher supersonic ve- 
locity would increase the proportion of early 
functions. Therefore, firing fuzed rockets from 
airplanes, though a more difficult procedure, 
seems to be the only reliable procedure to use in 
any further study of the phenomenon that may 
be undertaken. 

Performance in Firing for Function 
On Approach to Water 

The performance of T-30 fuzes fired from a 
ground launcher for function on approach to 
a water surface is summarized in Table 12. 
The summary for fuzes fired from a plane for 
function on approach to water is given in Table 
13. Burst heights are included as a matter of 
general interest in Table 13, although they are 
of secondary significance in connection with the 
intended air-to-air application of the fuze. Re- 
sults obtained with fuzes with different ampli- 
fier characteristics (indicated by the frequency 
of maximum gain [PkAF] ) are pooled in 
Table 12, since there was no evidence of any 
effect of this difference on the scores. Burst 
heights are affected by PkAF and are, there- 
fore, not given in this table. 

It should be noted that the velocity of the 
light AR 3.5 (AR 3.5 with the special 4-lb 
shell) is about the same as that of the HVAR, 
while the regular AR 3.5 and AR 5 are pro- 
gressively slower (in the order named). Ac- 
cording to experienced observers, afterburn- 
ing is most pronounced ^vith respect to both in- 
tensity and duration in the HVAR. 

In examining the high-angle test results in 
Table 12, it will be noted that although the dud 
scores are a little high, they are not excessively 
so in comparison with most production model 
VT fuzes. For equal flight times (quadrant ele- 
vations), middle functioning is markedly 
greater on the HVAR than on the light AR 3.5. 
A rational explanation is provided by the pro- 
longed afterburning of the HVAR Early func- 
tioning is uniformly about 20 per cent on the 
high-speed rockets, and significantly less on the 
regular AR 3.5. The excess on the light AR 3.5 
is most plausibly associated with the greater 


intensity of mechanical vibration of the rocket 
that is to be expected at the higher speed. If the 
difference were accounted to electric disturb- 
ances caused by the higher generator speed, a 
still greater excess of early functions might be 
expected on the HVAR, where afterburning is 
so prominent. 

Since 5 sec may be taken as a maximum use- 
ful flight time for plane-to-plane firing, it is 
reasonable to combine the middle-function 


Table 12. Performance in high-angle firing. 


Reference 

number 

Number 

fired 

Per cent 

P E M 

D 

Quadrant 

elevation 

(degrees) 

57 

252 

AR 3.5 

83 9 

2 

6 

30 

58 

122 

HVAR 

55 20 

22 

3 

55 

59 

112 

AR 3.5* 

64 19 

9 

8 

55 

60 

216 

AR 3.5* 

55 21 

18 

6 

70 


* AR 3.5 with a special 4-lb shell for testing VT fuzes. 


scores with the proper-function scores. The 
data in Table 12 then give rather uniform 
proper-function scores of 73 to 77 per cent on 
the high-speed rockets. A reliability of about 
75 per cent is thus indicated for rounds well 
within the radius of action of an airplane target 
at extreme range. 

Special comment is needed on the results of 
plane-to-water firing given in Table 13, and it 
may as well be admitted at the outset that most 
of the data would have been omitted had there 
been anything more reliable to offer for study. 
The first three lines of data in this table repre- 
sent results obtained with six missions of eight 
rounds each. Subsequent high-angle firing, and 
the test summarized in the last entry in the 
table, gave a very strong indication that the 
excessive dud scores were due to the use of 
Fahnstock clips on the arming wires (some of 
which were reported broken after these tests). 
Unfortunately, carrier observations were not 
made in the initial test, so that it was not pos- 
sible to localize sharply the source of the 
trouble. The differences between the first three 
dud scores may be due to the differences in the 


SECRET 


NAVY ROCKET FUZES 


383 


Table 13. Performance of T-30 in plane-to-water 
firing. 64 * Flight time, 4 to 5 seconds. 


Number 

Per cent 

Mean 

burst 

Standard 

error 

PkAF 

fired 

P E D 

height 

(ft) 

mean 

(ft) 

(c) 


AR 3.5 Dive angle 30-50° ; dive speed 235-250 mph 

16 75 0 25 104 5 77 


AR 3.5* Dive angle 30-50° ; dive speed 235-250 mph 

16 100 0 0 95 4 77 

AR 5.0 Dive angle 30-50° ; dive speed 235-250 mph 

16 50 6 44 102 6 77 

AR 5.0 Dive angle 40° ; dive speed 320 mph 

23 91 9 0 325 17 100 


* AR 3.5 with a special 4-lb shell for testing VT fuzes. 

initial accelerations of the three rockets. How- 
ever, the differences cannot be regarded as 
having much statistical significance in view of 
the fact that there were only six missions and 
in view of the likelihood that the arming wire 
installations were probably fairly uniform for 
each mission. 

If it were not for the possibility that some of 
the duds were due to the “dumping” phenome- 
non, one might adjust the dud scores to be equal 
to the average of the values given in Table 12. 
However, the only safe conclusion is that there 
is no inconsistency between the plane-to-water 
firing results, and the high-angle firing results 
when due allowance is made for duds caused by 
the use of Fahnstock clips on arming wires in 
some of the plane-firing tests. 

Performance in Firing at a 
Fixed Mock-Plane Target 

There were a number of mock-plane tests at 
Blossom Point, using various rockets and vari- 
ations of fuze design. Many of the tests were 
made, using modified T-50 fuzes 27 before T-30 
models had been constructed. Shortly after a 
satisfactory design for the T-30 had been de- 
veloped, emphasis was shifted to the T-2004 for 
air-to-ground firing; hence, only a small num- 
ber of rounds were fired against the mock plane 
with the final design of T-30. 

The results of T-30 target tests are given in 
Table 14. In order to indicate the radius of 


action there are included the observed impact 
parameters p of trajectories defined as 

p max = distance in feet of the farthest tra- 
jectory from the target for target functions. 

p min = distance in feet of closest trajectory 
to the target for any fuze that functioned far 
beyond the target. 


Table 14. Performance in firing at a fixed mock- 
plane target. 


Pro- 

jectile 

Number 

fired 

P 

Per cent 
E L 

D 

V 

Max 

Min 

PkAF 

AR 5.0 

20 

65 

0 

30 

5 

74 

72 

100 

AR 3.5* 

20 

40 

5 

50 

5 

98 

70 

100 

AR 3.5* 

20 

60 

0 

20 

20 

101 

lOlf 

76 

AR 5.0 

20 

65 

0 

20 

15 

98 

89f 

78 


* AR 3.5 with a special 4-lb shell for testing VT fuzes, 
f Two fuzes which passed the target at 33 and 34 ft respectively 
and later functioned on approach have been omitted from considera- 
tion. These were either unusually insensitive or were not armed at 
the target because of possible dumping of the firing condenser. 

Spot charts showing the position and dis- 
tance of closest approach (impact parameter) 
of all target and passage functions may be 
found in reference 29. 

Fuzes with amplifiers peaked at 100 c appear 
to have a radius of action of approximately 70 
ft; fuzes with peak frequencies of 77 c show a 
radius of action of approximately 90 ft. Except 
for the two rounds which passed the target at 
33 and 34 ft, the bulk of the live rounds which 
passed the target without firing began at 70 or 
90 ft respectively. The results for fuzes with 
trajectories within the radius of action are as 
follows : 

PkAF , 100 c; radius of action, 70 ft 
N P E L D </cP 

16 15 0 0 1 94 

PkAF, 77 c; radius of action, 90 ft 
N P E L D %P 

29 22 0 3 4 76 

The almost complete absence of early func- 
tions, shown above, is to be attributed to the 
short distance from projector to target (1,200 
ft). 

Performance in Plane-to-Drone Firing 

Firings against a drone were conducted at 
the Naval Ordnance Test Station at Inyokern. 
The T-30 fuzes on AR 5.0 and AR 3.5 were 


fSECHET 



384 


ANALYSIS OF PERFORMANCE 


ripple fired from a torpedo bomber [TBM] 
equipped with four zero-length rails, against a 
TDR drone. 42 Spotting charge-loaded as well 
as HE-loaded rounds were used. Precise meas- 
urement of burst positions was impossible be- 
cause of the test conditions. The firing was done 
from about 375 yd astern of the drone at speeds 
of 160 knots (pursuit) and 95 knots (target 
plane). It should be noted that, although the 
maximum speed and the reflection properties of 
the drones employed are somewhat different 
from those of combat planes, the test condi- 
tions were much more like those of combat than 
any other tests performed with this fuze. Re- 
sults of the Inyokern tests are given in Table 
15. 


Table 15. Performance in plane-to-drone firing. 


AR 3.5 

AR 5.0 


spotting 

spotting 

AR 5.0 

charge 

charge 

HE-loaded 


Early (%) 

0 

5 

17 

Passage without function 
(%) 

12 

34 

33 

Proper (%) 

88 

61 

50 

Number fired 

24 

61 

6 

Mean distance of propers 
from target (ft) 

45 

48 

21 


Several drones were destroyed by the HE- 
loaded rounds. It was obviously impractical to 
destroy enough drones to obtain a reliable 


not be calculated by the usual means. However, 
the conditions of the test were such that the 
radius of action would be expected to be 
roughly 50 per cent greater than the mean dis- 
tance of proper functions. Considering the 
assumptions involved in estimating the radius 
of action in this way, the 70-ft value so ob- 
tained is in satisfactory agreement with the 
estimate of 90 ft from the fixed target tests. A 
comparison of proper function scores cannot be 
made, since the number of rounds within the 
radius of action of the drone is unknown. 


934 Performance of T-2004 Fuzes 

The T-2004 is designed for use on rockets 
fired from a plane against targets on land or 
water. It has, therefore, been possible to test 
this fuze under the conditions of its tactical use. 
However, because of the greater convenience, 
the larger part of the proof testing has been 
done by firing from a stationary launcher for 
function on approach to water. Results of ex- 
perimental high-angle firing tests are summar- 
ized in Table 16. Results of experimental plane- 
to-surface firing tests are summarized in Table 
17. Most of the tests in Tables 16 and 17 in- 
volved pilot-production models with a number 
of variations in arming delay resistance, gen- 
erator shaft couplers, and thrust bearing. 


Table 16. Performance in experimental high-angle firing. Target factor: 81. 









Standard 


Approximate 





Mean 

error 

Reference 

flight time 

Number 


Per cent 


burst height 

mean 

No. 

(sec) 

fired 

P 

E M 

D 

(ft) 

(ft) 


61 

26 

288 

AR 3.5, quadrant elevation 30° 
92 4 1 

3 

18 

0.4 

62 

18 

20 

AR 5.0, quadrant elevation 30° 
85 0 0 

15 

19 

1.1 

63 

31 

25 

HVAR, quadrant elevation 30° 
64 20 4 

12 

33 

1.9 

64 

47 

24 

AR 3.5, quadrant elevation 70° 
92 4 0 

4 

19 

1.2 


measure of the probability of so doing. The 
weighted overall mean distance of the proper 
functions is 46 ft. Since the passage distances 
could not be measured, the radius of action can- 


Acceptance tests of the production model 
T-2004 fuzes were conducted on the AR 3.5 
according to the procedure outlined in Section 
9.8. Results are summarized in Tables 18 and 


NAVY ROCKET FUZES 


385 


20. In all cases where the target factor (reflec- 
tion coefficient in per cent) is given as 81, the 
target was a water surface. Acceptance testing 
was done at Aberdeen (target factor 81) and 
Jefferson Proving Grounds (target factor 65). 
Target factors for firing against ground at 
Dahlgren and Inyokern are unknown. 


so rare that the available data are insufficient 
to give a reliable time distribution. The accept- 
ance test data do show, however, that the inci- 
dence of functions from arming up to 5 sec is 
roughly ten times as great as it is during any 
later equal period. The 5-sec limit may, there- 
fore, be regarded as a useful one, even though 


Table 17. Performance in experimental plane-to-surface firing. 43 - 64b 


Approximate 
flight time 
(sec) 

Number 

fired 

P 

Per cent 
E 

D 

Mean 

burst height 
(ft) 

Standard 
error mean 
(ft) 

Target 

factor 



HVAR, 30 ° dive, plane speed 320 mph 



2 

8 

12 

0 

88 

32 


Land 

3 

16 

63 

6 

31 

64 

4.7 

81 



U.5" T-87, 30° dive, plane speed 250 mph 



8 

20 

85 

0 

15 

32 

1.2 

81 



AR 5.0 , 30° dive, plane speed 310-3 40 mph 



3 

40 

86 

2 

12 

33 

1.4 

81 



AR 5.0, 40° dive, plane speed 345 mph 



4 

79 

94 

3 

3 

27 


Land 


Inspection of the tabulated flight times 
shows that the time available for middle func- 
tioning was very limited in the plane-firing 
tests, and no such functions were recorded in 
the tests of Table 17. In several of the tests 
summarized in this table, there was a very lim- 


its significance in relation to afterburning is 
not well defined. 

It should be noted that the classification, 
“late” (functions below 10 ft), used in the ac- 
ceptance tests, is a carry-over from the accept- 
ance testing of bomb fuzes (see Section 9.4). 


Table 18. Performance of T-2004 in metal parts acceptance tests. 


Lot- 

group 

No. 

Approximate 
flight time 
(sec) 

Number 

fired 

Per cent 

P E M L D 

Mean 

burst height 
(ft) 

Standard 
error mean 
(ft) 

Target 

factor 

1 

26 

817 

Quadrant elevation 30° 

90 1 1 2 6 

32 

0.4 

81 

2 

7 

100 

30° dive, plane speed 250 mph 
88 2 2 1 7 

47 

1.8 

81 

3 

19 

877 

Quadrant elevation 20° 

95 2 1 0 2 

28 

0.3 

65 

4 

34 

87 

Quadrant elevation 42° 

92 6 0 0 2 

17 

0.6 

65 

5 

6.5 

83 

20° dive, plane speed 290 mph 
98 0 0 0 2 

32 

0.7 

65 


* See Table 19 for identification of lots. 


ited opportunity even for early functions. In 
this connection it should be noted that the 
5-sec time limit used in the classification of 
early functions of the Navy rocket fuzes is a 
carry-over from the testing of the T-5 Army 
rocket fuze. Malfunctioning of the T-2004 is 


This classification was not used in the experi- 
mental tests in which either the Army or Navy 
rocket fuzes were fired for function on ap- 
proach to a ground or water target. The accept- 
ance usage was based on considerations of mili- 
tary utility rather than on the existence of any 


386 


ANALYSIS OF PERFORMANCE 


discontinuity in the function height distribu- 
tion (see Section 9.1.3). 

Proper functioning performance on the AR 
3.5 ranges from 88 to 98 per cent in the tables. 
Information on performance on the AR 5.0 is 
limited to pilot production models, and per- 
formance is not quite as good, averaging about 
90 per cent proper functions. The deficiency is 
due mainly to the rather high incidence of duds. 
This may easily be attributable to difficulty 

Table 19. Composition of lot groups in Table 18. 

Lot 

group 

No. Metal parts lots 

1 1001-1060 excluding lots ending in the 
digit 8 

2 1008, 1018, 1028, 1038, 1048, 1058 

3 1061-1066, 1072A, 1074A, 1075-1097, 1099, 

1100-1107, 1109-1117, 1119-1122 

4 1067, 1069, 1074 

5 1068, 1078, 1088, 1098, 1108 


with detonator contact spring adjustments. 
There is evidence of a progressive reduction in 
dud scores throughout production, as shown in 
Table 18. This parallels experience with bomb 
fuze production as shown in Section 9.4.3, 
where the phenomenon is discussed more fully. 
There is no known reason why performance 
should be better on the AR 3.5 than on the 
AR 5.0, and it is probably quite safe to take 
the acceptance data as representing the relia- 
bility of the fuze on both rockets. 

Table 20. Performance of T-2004 in ammunition 
lot acceptance tests. Quadrant elevation: 20° in 
most cases; target factor: 81; lots: 315-2 through 
315-20. 


Approxi- 
mate Mean Standard 

flight burst error 

time Number Per cent height mean 

(sec) fired P E M L D (ft) (ft) 

19 177 94 2 1 1 2 32 1.1 


Scoring performance on the HVAR is con- 
servatively represented by the data in Table 16, 
since a short RC arming delay (0.75 megohm, 
1.0 mf) was used in the test. The same delay 
was used in the HVAR tests given in Table 17. 


These results have little significance except for 
very short flights. 

It is not possible to make a satisfactory com- 
parison of observed with predicted burst 
heights on account of the absence of reliable 
terminal ballistic data on VT-fuzed Navy rock- 
ets. Approximate calculations indicate that, as 
in the case of bomb fuze burst heights, there 
are some inconsistencies in the burst heights 
recorded for the different test conditions in 
Table 18. None of the discrepancies is serious, 
however, and a fuller discussion is unwarranted 
here. 

Particularly interesting data on burst 
heights were obtained in the Naval Ordnance 
Test at Inyokern, 43 in which some of the fuzes 
were fired from a plane in ripple salvo on 
HE-loaded rounds. Results are summarized 
graphically in Figures 9 and 10, in which some 
acceptance data are added for comparison. In 
the test at Inyokern, all burst heights were 
measured photographically, and they are prob- 
ably more accurate than those estimated with 
the camera obscura in acceptance testing. 

There is no systematic evidence of sympa- 
thetic functioning of HE-loaded rounds fired in 
ripple salvo. In general character, the results 
resemble very closely those obtained in similar 
tests with the Army rocket fuzes. The main 
difference is that the T-2004 burst heights are 
lower (with due allowance for reflection coeffi- 
cient), since the fuze was designed to have a 
lower overall sensitivity in order to avoid ex- 
cessive burst heights. 


9 4 BOMB FUZES 

9,4,1 Introduction 

This section presents the results of bomb- 
fuze testing, both experimental and acceptance. 
Results are based in so far as possible on per- 
formance of production model units; only in 
cases where data from such units are inade- 
quate are they supplemented by those of earlier 
models. 

It will be noted that certain tables in this 
section are exceedingly brief. Although a much 
greater amount of testing was done (which 


BOMB FUZES 


387 


was more or less pertinent to some of the sub- 
jects discussed) than is shown in the tables, 
much has been eliminated in an effort to keep 
the data free from extraneous factors. For 



Code 

o 

□ 

0 


Range 
1,500 yd 
2,000 yd 
1,500 yd 
2,000 yd 


Explosive 
Spotting charge 
Spotting charge 
High explosive 
High explosive 


Vertical bar indicates ± one standard error of mean. 

Figure 9. Burst height as function of dive 
angle, T-2004 on AR-5 for indicated mode of 
firing. 

example, Table 27 in Section 9.4.3, showing the 
effect of vehicle on performance, includes data 
for one type of fuze only, since data on other 
fuzes were complicated by variations in release 
altitudes or plane speeds. It is to be understood 
that the pertinent data that are omitted show 
satisfactory general agreement with engineer- 
ing prediction but are unsuitable for analytical 
purposes. 

In the evaluation of performance the fol- 
lowing classifications of functions are used : 

Proper (Pw). A proper function is one occur- 
ring because of interaction between the fuze and 
the target. In acceptance work, definite arbi- 
trary limits on heights were set (see appendix 


to this chapter). For scoring of experimental 
rounds a less rigid criterion was used. Func- 
tions occurring within about twice to one-third 
the mean burst height of those definitely “on 
target” were scored as proper. 

Low or Late (L). A low function is one 
occurring below the lower limit set for proper 
function. 

Early (E). An early function is one occur- 
ring too soon to be called proper. 

Dud (D). A round in which no function 
occurs is classified as a dud. 

Note that all results are for release in level 
flight unless specified otherwise. 



Code 

A 

B 

C 

D 


Dive 

angle 

55°-60° 

40° 

20°-25° 

30° 


Speed 

(mph) 

350 

350 

350 

310-340 


Range 

(yd) 

1,500-2,000 

1,500-2,000 

1,500-2,000 

700-1,700 


Proving 

ground 

Inyokern 

Inyokern 

Inyokern 

Dahlgren 


Figure 10. Cumulative burst height distribution 
for various dive angles, T-2004 on AR-5. 

9 * 4,2 Safety and Arming 

General Remarks 

A great deal more attention was given to 
tests of the arming characteristics of bomb 
fuzes than in the case of other fuzes. The ex- 


388 


ANALYSIS OF PERFORMANCE 


perimental data on this subject are very volu- 
minous. An exhaustive analysis of arming per- 
formance is given in reference 22. The prin- 
cipal results of this analysis are summarized in 
this section. The basic data on arming per- 
formance may be found in detail in reference 
65. 

The extensive testing on the arming mecha- 
nism was primarily due to 

1. The compromise between two contradic- 
tory objectives. The first objective was to post- 
pone arming as long as possible in order (a) 
to protect the bombing plane from fragments 
from bombs exploding upon arming, or (b) 
to prevent the fuze from operating on other 
friendly planes in a deep formation. The second 
objective was to have arming occur as soon as 
was reasonably safe in order to allow level or 
dive bombing from low altitudes. 

2. The inherent spread in arming values due 
either to conditions of use or variations in man- 
ufacturing tolerances. 

The method of operation of the arming 
mechanism has been described in previous 
chapters (cf. Chapters 4 and 5). Here we are 
concerned primarily with the results of tests 
on the overall mechanism and of tests on the 
effect of the different parameters which cause 
variations in arming, i.e., (a) effective pitch 
of vanes of the windmill, (b) effective airflow 
around the nose of the bomb, (c) angular rota- 
tion of the detonator rotor to arming, and 
(d) reliability of the detonator contacts and 
the rotor locking pin. 

Pertinent Features of the 
Arming Mechanism 

1. Air Travel. The windmill-driven arming 
mechanism yields air-travel-to-arming for a 
given bomb and rotor-setting which is roughly 
independent of altitude of release and plane 
speed. 

Effect of Release Altitude. To within the de- 
gree of experimental accuracy necessary for 
determination of rotor-settings, the air-travel- 
to-arming has not been found to be affected by 
the variation in air density between different 
altitudes of release (3,000 to 20,000 ft). In any 
event the most precise data are required only 
for the low-level bomb releases, such as are 


used for rotor-setting calibration tests ; 
changes caused by higher altitudes are not im- 
portant on account of the added safety avail- 
able through use of the delayed arming device. 
Further consideration of high-altitude releases 
is given later in this section. 

Effect of Plane Speed. Variations in plane 
speed have somewhat greater effect. Wind tun- 
nel calibrations of vane speed versus wind 
speed performance of various windmills and 
turbines indicate a decrease in air travel at 
higher plane speeds. For the 10-bladed metal 
vanes and 3-bladed plastic vanes, the effect is 
less than the normal spread between units re- 
leased under similar conditions (less than 3 
per cent per 100-mph change in plane speed on 
the average). For the turbine-driven type, in- 
creasing the plane speed from 200 to 300 mph 
appears to decrease air travel by about 10 per 
cent, while a decrease to 150-mph plane speed 
results in a 15 per cent increase. It should be 
remembered, however, that the separation be- 
tween the bomb and the launching aircraft is 
less at the higher airspeeds, even with the 
same air travel for the bomb. For example, 
after 4,000 ft of air travel, the separation 
between plane and M-30 test bomb is 2,100 ft 
at 200-mph release but only 1,250 ft at 300-mph 
release. The last fact is more important from 
the point of view of safety than the relatively 
smaller change in air-travel-to-arming. 

Effect of Bomb. The air-travel-to-arming for 
all fuze types is greatly modified by the aero- 
dynamic characteristics of the bomb. The air- 
flow about the nose of the vehicle affects the 
rotational speed of the windmill or turbine to 
a much greater extent than it influences the 
trajectory of the bomb. For example, the tur- 
bine-type fuzes (T-82) on a large bomb (M-66) 
may travel more than twice the distance to 
arming than on the small test bomb (M-30) 
with the same rotor setting. This fact is quite 
consistent with safety requirements. Data on 
air travel ratios between various bombs is 
given in a later part of this section, under 
“Arming Performance of Typical Fuzes.” 

2. Operation and Use; Rotor Setting Methods. 
Setting of the rotors is accomplished by either 
of two methods: (a) counting of vane revolu- 
tions from the electric arming position or (b) 


BOMB FUZES 


389 


measuring the angle of the slot in the slow- 
speed shaft from the mechanical arming posi- 
tion. In the first method the vanes are rotated 
backward from the electric arming position by 
an electric motor attached to a mechanical 
counter. Electric continuity provides an indica- 
tion of the electric arming position. In the sec- 
ond method, the angle between the slot in the 
slow-speed shaft and a reference point on the 
rotor housing collar is set according to the indi- 
cations of a mechanical gauge. Knowledge of 
the reduction ratio of the gear train and the 
angular separation between the slot in the 
slow-speed shaft and the reference point on the 
housing collar, when the rotor is in the electric 
arming position, allows conversion of setting 
specifications from one system to another. Com- 
parative merits of the two methods are dis- 
cussed in reference 22. 

Methods of Release; Low Altitudes. Fuzes 
are supplied with an arming pin which blocks 
rotation of the vanes. The arming pin is held 
in place (while in the bomb bay) by the free 
end of an arming wire, the other end of which 
is fastened to the plane. When the bomb is 
dropped, the arming wire pulls out of the arm- 
ing pin, releasing it and permitting the vanes 
to rotate in the wind stream. 

Methods of Release; High Altitudes; Use of 
Arming Delay Device T-2. The arming mech- 
anism of the fuze proper is not generally set to 
give air-travel-to-arming greater than about 
4,000 to 5,000 ft. When air travel in excess of 
this is desired, a supplementary arming delay 
device (T-2) is employed (see Figure 1, Chap- 
ter 4). This device prevents expulsion of the 
vane blocking pin until the bomb has fallen 
through a predetermined distance along its tra- 
jectory. The device may be adjusted manually 
to yield up to 20,000 ft of additional air-travel- 
to-arming for the fuze. 

Settings for Given MinSAT 

Statistical Method. In the production of VT 
bomb fuzes, the determination of rotor settings 
has been based on the requirement of a specified 
minimum safe air -travel-to-arming [MinSAT] 
on the smallest bomb on which the fuze is to be 
used (M-30 in most cases). This MinSAT may 


be defined ideally as a lower limit , below which 
no fuze will ever become armed. Owing to vari- 
ations within the range of currently permissible 
manufacturing tolerances, the air-travel-to- 
arming for an individual fuze from a given lot 
may be found to differ from the mean value for 
the lot by as much as several hundred feet when 
dropped in the field. It is not practicable, there- 
fore, to set the fuze rotors so as to yield a mean 
air travel equal to the specified MinSAT, since 
in that case about half of the fuzes would be- 
come armed before traveling the MinSAT. Ac- 
cordingly, a safety factor is introduced in the 
form of a tolerance distance to be added to the 
MinSAT in order to obtain the mean air travel 
for which the rotors should be set. 

To establish the proper value for this toler- 
ance distance, it is necessary to determine the 
relative frequency of occurrence of units with 
air travel short of the mean by any given 
amount. The functional form of this distribu- 
tion of frequency may be developed mathe- 
matically from the assumption that a given 
deviation from the mean air travel is caused by 
the random superposition of a great many 
small independent deviations, each presumably 
due to a variation of some physical characteris- 
tic of the fuze from its average value for the 
lot. The frequency distribution resulting from 
these assumptions is the normal error law, 
which the observations appear to follow quite 
closely. This law does not, however, define an 
absolute lower limit for the possible values of 
air travel. In practice, therefore, the ideal defi- 
nition of MinSAT given above must be modified 
to denote a limit below which only a certain 
negligibly small percentage of the units become 
armed. With sufficiently large test samples, 
the location of this limit for any given produc- 
tion lot could be determined by a count of the 
units of extreme short air travel. Practically, 
however, such a procedure is inapplicable on 
account of the magnitude of the test samples 
that would be required. It is evident that in 
small test samples, units with extreme charac- 
teristics will seldom appear, and their scarcity 
will make direct count estimates of their prob- 
able frequency very unreliable. Such extreme 
units, however, are to be expected in much 
greater numbers in the much larger produc- 


390 


ANALYSIS OF PERFORMANCE 


tion lots. It becomes necessary, then, to infer 
their presence through an application of fre- 
quency distribution theory to observations on 
the more numerous, more nearly typical units 
of which the small test samples are mainly 
composed. 

This is accomplished by determining the ap- 
propriate numerical values of the dispersion 
parameter for the normal frequency distribu- 
tion (the standard deviation) from field test 
observations of samples of the various fuze 
types. The use of these values for extrapolation 
from the mean air travel, according to the 
theoretical distribution formula, then gives the 
air travel limit which only the selected negli- 
gible percentage of units will fail to exceed 
before arming takes place. The MinSAT is 
estimated from the mean air travel by the fol- 
lowing procedure. 

Consider the mean air travel as the sum of 
three quantities: (1) the MinSAT, (2) a mul- 
tiple of the standard deviation in air travel for 
the given fuze type, and (3) a supplementary 
allowance. 

1. The MinSAT is understood for this pur- 
pose to mean a fixed lower limit of air travel, 
below which only a negligibly small percentage 
of nondefective fuzes have a chance of arming. 

2. The multiple of the standard deviation 
represents a minimum permissible difference 
between the MinSAT and the mean air travel 
for the given lot corresponding to the adopted 
rotor setting. The selection of the multiple 
chosen is based on the condition that on the 
average, only 1 per cent of the individuals in a 
normally distributed population will deviate 
from the mean for the entire group by more 
than this multiple of their standard devia- 
tion. 

3. The supplementary allowance is included 
principally to account for probable differences 
between the mean air travel for the given lot 
corresponding to the adopted rotor setting and 
the mean air travel for the lot from which the 
test sample was drawn which determined the 
adopted rotor setting. This type of difference 
may be thought to originate from sources of 
variation which were not operating during the 
limited range of tests used for deriving the 
statistical parameters. Experience confirms 


the probable existence of such factors. To eval- 
uate the exact nature of such long-term pro- 
duction variations (which have the effect of in- 
creasing the expectation of large deviations) 
would require a program of more extended 
testing and wider scope than present practice 
includes. Continued need for the use of a sup- 
plementary safety allowance is indicated by 
the large deviations from the nominal test re- 
lease conditions which are likely to occur in 
actual service use. A liberal margin of safety 
(200 ft on the average) is generally allowed to 
compensate for all of these effects. 

The air travel limits between which certain 
specified percentages of fuzes may be expected 
to become armed are given in Table 21. 


Table 21. Air travel limits (ft) . 


Standard deviation of air 
travel (ft) 

100 

150 

200 

250 

MinSAT 

3,600 

3,600 

3,600 

3,600 

Mean air travel (50% 

armed) 

4,030 

4,145 

4,260 

4,375 

95^% armed 

4,200 

4,400 

4,600 

4,800 

Range: MinSAT to 95^% 

armed 

600 

800 

1,000 

1,200 


Estimates for other values of standard devia- 
tion of air travel may be made by interpolation 
in the table or by use of the formulas : 

Range (MinSAT to 95% per cent armed) = 
200 ft + 4.0 X (standard deviation of air 
travel) . 

MinSAT to mean air travel = 200 ft + 2.3 
X (standard deviation of air travel). 

Mean air travel to 95V2 per cent armed = 
1.7 X (standard deviation of air travel). 

For other values of MinSAT and for any 
vehicle, the standard deviation of air travel 
may be taken as approximately proportional to 
the mean air travel. 

Proving Ground Check. Proving ground tests, 
conducted for purposes of production quality 
control, are intended as an overall check on arm- 
ing performance under conditions simulating 
Service use as closely as possible. Specifications 
for loading acceptance tests for VT bomb fuzes 
(phase 1, see Section 9.8) provide that all of a 
sample of fuzes from a given lot dropped under 
certain plane speed and altitude conditions 


BOMB FUZES 


391 


(which correspond to an air travel to ground 
less than the rated MinSAT by certain tolerance 
amounts) must fail to function if the lot is to 
pass. Inspection criteria of this nature are in- 
dispensable for effectively guarding against oc- 
currence of defective units. Defective units are 
defined here as those subject to essentially un- 
predictable types of variation in air-travel-to- 
arming such as are caused by nonrandom ele- 
ments not covered in the overall method of 
analysis developed earlier in this section. Ex- 
amples of such exception factors are: (1) an 
improper choice of rotor setting, (2) a blunder 
in setting the rotor, or (3) the sudden appear- 
ance of some previously unencountered type of 
defect in a mechanical part. Frequency distribu- 
tion sampling theory, which presupposes a con- 
siderable degree of homogeneity in manufactur- 
ing production, is inapplicable to the prediction 
of such sources of error. 

The sampling technique employed for accept- 
ance testing depends simply upon the direct 
enumeration of infrequently occurring types, 
and, like all tests of this nature, provides little 
information on the probability of occurrence 
of similar rare types in other samples from 
similarly composed lots. This property, as 
already noted, is inherent in tests of this sort. 
It is an unavoidable consequence of the limita- 
tion imposed by the test design upon the num- 
ber of observable specimens with the charac- 
teristic about which information is sought. 
Furthermore, with the usual acceptance test 
procedure, the minimum permissible air travel 
that may be observed for a unit (before reject- 
ing the lot containing it) is not in practice 
rigidly fixed. Instead, the air travel limit de- 
fining a prematurely arming unit during any 
particular test may lie anywhere inside the 
range extending from the MinSAT distance to 
a point 350 ft in advance of it. This situation 
arises principally from the difficulty of main- 
taining a very stringent control over proving 
ground testing conditions. In addition, the ac- 
tual air travel measures (based on observations 
of time of flight or altitude of release) appear 
to be generally subject to large random errors, 
much greater than the variations which experi- 
mental field tests show may be properly at- 
tributed to the fuses themselves. It must be 


concluded, then, that while the acceptance tests 
are invaluable in screening out defective or 
improperly adjusted units, the data provide 
little information on the relative number of 
nondefective units expected to exhibit any par- 
ticular air travel to arming. In consequence, 
the acceptance test rejection record is not to 
be considered as a rigorous check on the ac- 
curacy of the specific predictions derivable 
from the MinSAT control theory presented in 
Section 9.4.2. Percentages of acceptances and 
rejections on the basis of air travel perform- 
ance are given in summary form in Table 22. 

Arming Performance of Typical Fuzes 

Mean Air Travel versus Rotor Setting. The 
rotor setting corresponding to a given mean air 
travel for a particular fuze type is determined 
by dropping a small sample of units from the 
production lot. The units are wired to fire a 
small explosive charge upon electric arming, 
which is thus made visible from the ground. 
Observation of the arming time and plane 
speed, combined with a knowledge of the bal- 
listic properties of the bomb, permit calculation 
of the air travel to arming for each unit. From 
these data, an estimate of the air travel per 
vane revolution under the given conditions is 
obtained, from which the rotor setting appro- 
priate to a specified mean air travel may be 
deduced. A description of the field testing pro- 
cedures is given in Section 8.2. 

The rotor calibration test procedure in prac- 
tice is beset by several difficulties. First, varia- 
tions in production standards between lots, 
which cannot be detected by calibration tests 
conducted on units all from the same lot, may 
introduce large apparent errors in the choice 
of rotor setting, revealed only when the units 
are subjected to the acceptance testing. This 
situation necessitates the addition of the 200-ft 
supplemental safety allowance discussed in 
Section 9.4.2 to all air travel settings. In addi- 
tion, the large variation of aerodynamic pitch 
(air travel per revolution) with wind speed for 
certain types may, if neglected, lead to serious 
errors in rotor setting estimates deduced for an 
air travel different from that for which the 
units were set during the calibration test. Wind 
tunnel observation of windmill speed at con- 


392 


ANALYSIS OF PERFORMANCE 


trolled wind speeds appears to be the only satis- set in order to conform with a specified 

factory solution for this problem. MinSAT requires a knowledge of the standard 

Typical rotor settings adopted for various deviation in air travel to be expected in Service 

fuse models may be found in data sheets in use of the fuze type (Section 9.4.2). Data use- 

Chapter 5. Approximate rotor settings may be ful for estimating this quantity are provided 
computed from the values of the air travel per by field tests such as are used for rotor setting 

Table 22. Acceptance (safety) test performance, phase 1. (A “safe” unit should fail to function.) 

Mfr. 

MinSAT 

(ft) 

Approx, air 
travel to 
ground* 

(ft) 

No. of 
units 
tested 

No. of 
functions 
observed 

Percentage 
of functions 
(failures) 

Approx, tolerance* 
(MinSAT minus 
air travel 
to ground) 

(ft) 

Emerson 

3,600 

3,500 

370 

2 

y 2 

+100 


3,600 

3,000 

80 

0 

0 

+600 


3,100 

3,300 

35 

3 

9 

—200 


3,100 

2,900 

120 

3 

2% 

+ 200 


2,600 

2,300 

20 

0 

0 

+300 


2,000 

1,800 

10 

0 

0 

+ 200 

Zenith 

4,500 

4,000 

55 

3 

5 

+500 


3,600 

3,600 

330 

3 

1 

0 

Philco 

3,600 

3,500 

315 

12 

4 

+ 100 


3,100 

3,100 

100 

6 

6 

0 


2,000 

1,900 

83 

0 

0 

+100 

GE 

2,000 

1,900 

100 

2 

2 

+ 100 

Simplex 

3,600 

3,500 

101 

3 

3 

+ 100 


3,100 

3,100 

20 

0 

0 

0 

All combined .... 


1,739 

37 

2 

+ 100 


* The air travel to ground (and tolerance distance) may be in error by several hundred feet. 


revolution observed for various vane types in 
the wind tunnel. Some results, corresponding 
to an air travel of about 4,000 ft, are given in 
Table 23. With bombs other than the one on 
which the calibration test was conducted, allow- 
ance must be made for the effect of the vehicle 
upon the vane speed and consequent air travel 


Table 23. Average values of air travel per vane 
revolution on M-30 bomb in wind tunnel (230-250 
mph wind speed). 


Fuze and vane type 

Air travel (ft) 
per vane 
revolution 

6-in. Bakelite vane, bar type 

1.20 

6-in. aluminum vane, bar type 

1.32 

9-in. Bakelite vane, medium antenna 

ring 1.32 

55° metal, thin antenna ring 

1.82 

Turbine, bar type 

1.47 


to arming. The approximate relative air travel 
for various type fuzes with the same rotor 
setting on different bombs is listed in Table 24. 

Spread in Air Travel. Determination of the 
mean air travel for which the rotors should be 


calibration. Further information may be de- 
rived from analysis of wind-tunnel fuze per- 
formance in combination with certain other 
laboratory measurements. Both methods pro- 
vide mutually consistent independent estimates 
of air travel spread for the various fuze types. 
The two procedures supplement each other, 


Table 24. Relative air travel on various bombs 
from field and wind tunnel data. 


Fuze 

type 


Bomb type 


Standard 
devia- 
tion of 

M-30 M-81 M-64 M-65 M -66 M-56 

ratios 

Ring and bar 
types, plastic 
and metal 

vanes 

1.00 

1.02 1.15 1.32 

1.58 

1.48 

±0.02 

Bar type, tur- 
bine vane 

1.00 

1.02 1.24 1.48 

2.32 

1.87 

±0.03 


i.e., field testing duplicates Service use condi- 
tions more directly while wind-tunnel test re- 
sults are less affected by experimental error. 
Comparative merits of various test methods for 


BOMB FUZES 


393 


determining air travel spread and application 
of observational data to their calculation are 
discussed in reference 22, in which numerical 
examples of air travel spread for various fuze 
types are given. A few typical examples for late 
production models (when set for 4,000-ft mean 
air travel) follow. 

Standard Tolerance 
deviation deviation 
(16% limit) (1% limit) 


Manufacturer 

Type 

(ft) 

(ft) 

Emerson 

T-90 

150 

350 

Zenith 

T-51-E1 

150 

350 

General Electric 

T-89 

175 

410 

Philco 

T-89 

230 

540 

Westinghouse 

T-82 

250 

580 


Examples of frequency distributions of the 
deviations from mean air travel to be expected 
of individual units may be found in reference 
28. Comparisons with the theoretical normal 
frequency law show sufficiently good agreement 
between the observed and theoretical distribu- 
tions to justify use of the normal law in calcu- 
lating MinSAT tolerances (Section 9.4.2). An 
example of such a comparison is given in Fig- 
ure 11. 



Figure 11. Distribution of deviations in air 
travel to arming for bomb fuzes and corre- 
sponding normal distribution fitted to data. 

Factors Affecting Consistency of Air Travel 
Performance. A brief discussion has already 
been given both of the principal fuze character- 
istics designed to produce constant air-travel- 
to-arming under a variety of field conditions 
and of the extent to which this requirement is 
found to be fulfilled in practice. There remain 
still to be considered the observed lack of con- 
stancy of air travel performance under con- 


stant field conditions and the principal factors 
causing these accidental differences between 
units of similar design. A comprehensive study 
of this phase of air travel performance, based 
largely on wind-tunnel observation, is con- 
tained in reference 22. 

1. Vane speed variations. Differences in air- 
travel-to-arming between fuzes set to perform 
identically under the same conditions are ac- 
counted for principally by differences in wind- 
mill or turbine speed. Variations in construc- 
tion of. the detonator contacts, which cause in- 
advertent differences in rotor setting under 
some circumstances, are secondary in impor- 
tance. The standard deviation in vane speed 
between units is found to be a certain fixed per- 
centage of the vane speed which is a character- 
istic of the unit type (model and manufac- 
turer) and is virtually unaffected by changes 
of vehicle or plane speed. This relationship 
leads to an approximate proportionality be- 
tween spread in air travel and mean air travel. 

The exact mechanical components of the gen- 
erator vane and shaft system in which lack of 
uniformity in manufacture is most effective in 
producing the observed spreads in vane speed 
have not been completely identified. Measures 
of generator shaft torques and of dimensions 
of certain external mechanical features of the 
fuzes have thus far accounted for only a negli- 
gible portion of the entire observed spread in 
air travel. 

The later revised production models of Emer- 
son and Zenith show a great reduction in ran- 
dom variations in vane speed between units. 
In wind tunnel tests, these types performed 
with vane speed standard deviations (and par- 
tial air travel standard deviations thereby in- 
duced) of about 1^/2 Per cent. Under the same 
conditions, regular production models by the 
same manufacturers exhibited almost twice 
this spread, while variation in other manufac- 
turers’ models ranged up to three or four times 
as much. 

2. Rotor setting errors. The next most im- 
portant factor in causing spread in air travel is 
a lack of uniformity in detonator contact spring 
construction which leads to random setting 
errors in rotor-shaft arming angles. This cir- 
cumstance introduces an increase in the stand- 


394 


ANALYSIS OF PERFORMANCE 


ard deviation of air travel over that due to 
vane-speed variation ranging from about 15 
to 30 ft. Errors in the actual gauging of the 
shaft angles contribute only a minor portion 
of this quantity. 

3. Testing errors. Another important consid- 
eration is the experimental field test observa- 
tional error, which is responsible for a further 
(apparent) increase in standard deviation of 
air travel amounting to from 10 to 30 ft, the 
effect being the greater for the better models 
and shorter air travels. The last-mentioned 
source of variation does not exist in actual op- 
erational use. It may be entirely eliminated 
by conducting the tests on the units in a 
wind tunnel, without danger of thereby in- 
troducing any new or more undesirable sources 
of error. 


9 4,3 Ring-Type Fuzes 

Performance under Acceptance 
Test Conditions 

General Remarks. The analysis of perform- 
ance of fuzes under acceptance test conditions, 
which provides the field performance data 
given in Section 5.5, is based on the metal parts 
acceptance tests. These tests were carried out 
on a much larger scale and under conditions 
much more like combat conditions than were 
the tests of the completely loaded fuzes, i.e., the 
ammunition lots (see Section 9.3.1 for defini- 
tions of metal parts and ammunition accept- 
ance tests) . Where the metal parts tests show 
significant variations in performance it would 
be possible, theoretically, to make some allow- 
ance for these variations in predicting the per- 
formance of the ammunition lots. However, the 
composition of ammunition lots is highly vari- 
able. The lot size ranges from a few hundred 
to several thousand fuzes, and a lot may con- 
tain from one to nearly a dozen metal parts 
lots, or fractions thereof, widely spread with 
respect to time of production. Furthermore, the 
loading of the fuzes is known to have intro- 
duced factors in one or two cases that were 
absent in the metal parts testing. Therefore, 
although the properties of the ammunition in 
its final form are of primary practical interest, 


it is not feasible to attempt a quantitative pre- 
diction of the effect of variations observed in 
metal parts testing. For this reason, and be- 
cause most of the statistically significant vari- 
ations are not of much practical importance, 
the data have not been analyzed as exhaustively 
as would be possible. 

In calculating the scores from acceptance 
test data, the scores obtained with rejected lots 
are included, since what is required is an esti- 
mate of the quality of the product. As with 
most sampling procedures, rejections were 
almost entirely the result of random sampling 
fluctuations, and elimination of the reject 
scores would yield an overestimation of the 
quality of the fuzes. 

For the sake of simplicity, the Army Ord- 
nance designations for the complete fuzes are 
used in discussing the performance of the metal 
parts assemblies, although strictly speaking 
the Signal Corps system of AN/CPQ desig- 
nations should be used (see Section 5.5). 

Conditions for Acceptance. The procedure 
for conducting metal parts acceptance tests is 
summarized as appendix material to this chap- 
ter in Section 9.8. The following test conditions 
hold except where deviations are noted : 

Nominal altitude of release: 10,000 ft. 

Nominal true airspeed at release: 200 mph. 

Test vehicle 

For Brown carrier fuzes: 

M-81 (260-lb) fragmentation bomb or 
M-88 (220-lb) fragmentation bomb. 

For White carrier fuzes: 

M-64 (500-lb) general purpose [GP] 
bomb. 

A double sampling formula was used with 
the proper functioning requirements stipulated 
so that a negligible fraction of the metal parts 
lots would be rejected as long as the manufac- 
turing quality was above an 80 per cent proper- 
functioning level. 244 

Summary of Data for Various Groups of 
Lots. In Table 25 there is given the average 
score and function height for each of several 
groups of metal parts lots of each of the fuzes. 
The lot group number (first column) is used 
for reference purposes in the discussion, and 
to identify the metal parts lots to which the 
data apply, with the aid of auxiliary Table 
26. 


SECREf' 


BOMB FUZES 


395 


For the most part, the reason for the group- Where it is not apparent in the table, the 

ing of the lots is apparent, namely, differences reason for the grouping is given in the discus- 
in plane speed, or target factor. The target sion of the performance of the fuzes, 
factor (second column) is the reflection coeffi- Effect of Test Conditions on Performance. 

cient of the terrain expressed as a percentage. There is no reason to anticipate any perceptible 
It is to be understood that the target factor is difference in scores on account of a 40-mph dif- 

Table 25. Metal parts acceptance test results. 








Mean 

Standard 

Lot 


Number 




burst 

error 

group 

Target 

units 


Per cent 

score 


height 

mean 

No. 

factor 

tested 

P 

L 

E 

D 

(ft) 

(ft) 




Brown carrier fuzes 







T-50-E1 and 

T-89 (Philco) 




1 


542 

79 

0 

15 

6 

34 

0.7 

2 

Ice 

226 

83 

0 

14 

3 

32 

1.0 

3 

65 

76 

90 

0 

9 

1 

37 

2.0 




T-50-E1 (Philco-Simplex) 




4 


387 

85 

0 

11 

4 

37 

0.9 

5 

Ice 

47 

81 

2 

17 

0 

32 

2.2 




T-91 (Philco) 





6 


42 

76 

0 

26 

0 

44 

3.6 

7 


204 

83 

1 

11 

5 

29 

0.4 

8 

65 

680 

89 

0 

10 

1 

39 

0.6 

9* 

65 

37 

78 

0 

20 

2 

36 

1.9 




T-91 

(GE) 





10 


499 

80 

0 

12 

8 

41 

0.9 

11 

65 

53 

89 

0 

4 

7 

43 

1.7 

12* 

65 

259 

89 

0 

6 

5 

55 

1.2 

13* 

60 

106 

87 

0 

10 

3 

55 

1.9 




M-168 (T-91-E1) (Emerson) 




14* 

65 

289 

93 

0 

6 

1 

59 

1.2 

15* 

55 

170 

92 

0 

8 

0 

55 

1.3 




White carrier fuzes 







T-50-E4 (Emerson) 




16 


370 

80 

1 

17 

2 

35 

0.9 

17 


680 

75 

2 

17 

6 

45 

1.0 

18 


279 

82 

1 

14 

3 

34 

1.1 

19 

Ice 

72 

71 

0 

28 

1 

32 

3.0 

20 


736 

75 

1 

22 

2 

38 

0.8 

21* 

65 

16 

82 

0 

18 

0 

58 

4.7 




T-92 (Emerson) 





22 


1,000 

57 

1 

34 

8 

33 

0.7 

23* 

65 

34 

59 

0 

29 

12 

48 

4.0 




T-92-E1 (Emerson) 




24 

65 

22 

95 

0 

0 

5 

39 

3.1 

25* 

65 

63 

75 

0 

24 

1 

48 

2.3 

26 


17 

76 

0 

18 

6 

39 

4.8 


* 240 mph nominal true airspeed at release. 


approximately 81 (water surface at Aberdeen 
Proving Ground) unless otherwise stated 
(other numerical values apply to Jefferson 
Proving Ground). The reflection coefficient of 
ice depends upon a number of conditions which 
were not recorded in detail for these tests. 


ference in plane speed, and an inspection of 
Table 25 shows no consistent indication of such 
a difference. 

With the rather wide limits of burst height 
that were used in the classification of proper 
functions, no perceptible effect of target factor 


396 


ANALYSIS OF PERFORMANCE 


on score would be anticipated, and none is ob- 
served in the table. 

These conditions (plane speed and target 
factor) are therefore disregarded in estimat- 
ing the overall score for each fuze. 

Table 26. Identification of lot group numbers 
listed in Table 25. (Duplication in lot number in- 
dicates part of the lot was tested under conditions 
of the particular group number.) 


Lot 

group 

No. 

Composed of metal parts lots 

1 

CPR 43 through 59, 62 through 79, 102, 104, 
106 

2 

CPR 80 through 101 

3 

CPR 108, 110, 112, 114, 116, 118, 140 

4 

CPR IS through 23S, 25S, 29S, 30S 

5 

CPR 24S, 26 S, 27S, 28S 

6 

CPR 103, 105, 111 

7 

CPR 166 through 177 

8 

CPR 107, 109, 113, 115, 117, 119, 120 through 
139, 141 through 155, 157 through 165 

9 

CPR 178 through 180 

10 

CG 1 through 23 

11 

CG 24, 25, 27, 31 

12 

CG 27 through 39, 41, 44, 45 

13 

CG 40, 42, 43, 45 through 48 

14 

CEX 3001 through 3014, 3019, 3021, 3022 

15 

CEX 3015, 3018, 3020, 3023 through 3027 

16 

CEX 1 through 19, 21 

17 

CEX 20, 22 through 50 

18 

CEX 51 through 74 

19 

CEX 75 through 80 

20 

CEX 81 through 84, 86 through 104, 106 
through 109, 112, 113, 114, 116, 117, 118, 
120, 121, 122, 124, 125, 126, and all even 
numbered lots through 144, 148 

21 

CEX 146 

22 

CEX 105, 110, 111, 115, 119, 123, 127, and 
all odd numbered lots through 195, 201 

23 

CEX 205, 207 

24 

CEX 178, 184 

25 

CEX 182, 184, 176, 178, 180 

26 

CEX 174 


In considering the mean burst heights, the 
situation is different. Inspection of the pre- 
dicted isoburst height charts (Section 5.5) in- 
dicates that increasing the plane speed from 
200 to 240 mph should increase the burst height 
by something like 10 ft. The theory of opera- 
tion of the fuzes indicates that a reduction in 
reflection coefficient from 0.81 to 0.65 should 
reduce the burst height by 10 to 20 per cent 
or by something like 5 ft for these data. Such 
differences are large in comparison with many 
of the tabulated standard errors of mean burst 


heights, and one might therefore hope to ob- 
tain a good check on the predictions from these 
data. Unfortunately, there are present in the 
data certain variations in burst height that 
cannot be accounted for quantitatively. Atten- 
tion is called to specific cases presently. At this 
point it is sufficient to remark that these vari- 
ations are of a magnitude similar to the pre- 
dicted differences just mentioned. Therefore 
no precise check on the theory from these data 
is possible. 

In view of the presence of uncontrolled fac- 
tors in the data, it is very desirable to estimate 
the burst height performance from all of the 
data rather than from selected groups. If the 
effect of reflection coefficient (other than that 
of ice) is tested by determining burst-height 
ratios between lot groups for which all other 
conditions are presumably equal, and these 
ratios are weighted in accordance with the 
amount of data and averaged, it appears that 
on the whole the effect of target factor (other 
than ice) is nil. This same procedure indicates 
that the average target factor of ice, as it 
affected these tests, is about 92, a result which 
agrees with an unpublished investigation of 
this matter. The general conclusion is that some 
uncontrolled factors are present in the data 
that give burst heights at Jefferson Proving 
Ground that appear to be higher than would be 
expected from the Aberdeen data. This factor 
might be a difference in the systematic com- 
ponents of the errors in burst-height measure- 
ment at the two locations. In order to be con- 
servative in combining data to obtain overall 
average burst heights for each fuze, the effect 
of target factor (other than ice) is neglected. 

A like analysis shows that the overall aver- 
age effect of the 40-mph increase in plane speed 
is to add about 7 ft to the mean burst heights. 
This value is in reasonable agreement with 
engineering prediction and it is used in re- 
ducing all lot group mean burst heights to a 
200-mph basis before calculating average per- 
formance for each fuze type, although to be 
strictly correct a slightly different correction 
should be made for each fuze type. 

Performance of T -50-El and T-89. The first 
six lots of Philco production were tuned on a 
load equivalent to the M-64 bomb and gave 


BOMB FUZES 


397 


fairly satisfactory performance on this bomb, 
although an excessive number of duds was 
observed. The main cause for the duds had been 
found in the type-approval test to lie in faulty 
detonator contact springs. When these lots 
were tested on the M-81 bomb, a very large 
number of early functions was observed and 
production was halted temporarily. Specifica- 
tions were changed to require laboratory test- 
ing on a load equivalent to the M-30 bomb, and 
the amplifier was changed from the No. 8 to the 
No. 10 type, which became standard for the 
T-50-E1. 

Acceptance testing was resumed with the 
M-81 as a standard vehicle, but the dud per- 
formance remained poor through lot 42. Omit- 
ting retest scores (which would throw undue 
weight on exceptionally poor lots), the overall 
performance on M-81 for this series was 

Per cent Lots 


N 

P 

L 

E 

D 


491 

66 

0 

15 

19 

8-42 

102 

80 

0 

12 

8 

24, 27, 33, 35, 37, 42 


(reworked lots) 


The score for the six lots that failed the re- 
test and were subsequently reworked showed 
a significant but not entirely satisfactory re- 
duction in the occurrence of duds. The lots that 
were not reworked were, for the most part, 
loaded into ammunition lots through PA — 
180 — 15; reworked lots were loaded later. 

The performance of the balance of the T-50- 
E1 and T-89 production is given in Table 25, 
items 1 through 5. There are no markedly sig- 
nificant differences in these scores, which give 
an average of 

Proper 83 per cent 

Late 0 per cent 

Early 13 per cent 

Dud 4 per cent 

Number tested, 1,278 
Mean burst height, 35 ft 


able uniformity and give the following pooled 
estimates. 


Per cent 

Philco 

GE 

Both 

Proper 

87 

84 

86 

Late 

0 

0 

0 

Early 

11 

10 

10 

Dud 

2 

6 

4 

Number 

963 

917 

1,880 


In early GE production some difficulty with 
detonator contact springs caused a relatively 
large number of duds, but the situation was not 
serious enough to warrant special discussion as 
in the case of early T-50-E1 production. The 
Philco T-91 fuzes appear to have benefited from 
the special attention that had to be given to 
this problem in the earlier model. No T-91 
metal parts production lots were rejected. 

There is a rather large difference (15 ft) be- 
tween the mean burst heights of lot groups 6 
and 7, which cannot be explained by any dif- 
ference between the characteristics of the lots 
as measured in the laboratory. The only re- 
corded difference in test conditions that might 
be pertinent is in the test vehicle ; group 6 was 
tested on the M-81 and group 7 on the M-88 
bomb. However, there is no known difference 
between the properties of these bombs that is 
large enough to account for so large a differ- 
ence in burst heights. The observed difference 
is probably due to a chance combination of fac- 
tors, no one of which is alone sufficient to 
account for the difference in heights. Group 7 
appears to be more inconsistent than group 6 
with the other groups, 8 and 9, of Philco T-91, 
but there is no reason to reject it from the 
overall estimate of burst heights: 


Product 
T-91 (Philco) 
T-91 (GE) 
T-91 (both) 


Mean burst 
height (ft) 
37 
44 
40 


The burst height of the Simplex product is 
slightly higher than that of Philco but the 
difference is of little practical importance. The 
overall average burst height over Aberdeen 
water is 35 ft. 

Performance of T-91. The scores of the vari- 
ous lot groups of both Philco and General Elec- 
tric Company [GE] production show reason- 


The higher burst height of the GE fuzes may 
be due in part to greater r-f sensitivity (18 as 
compared with 16 v for Philco), but the un- 
accountably low burst height of Philco group 
7 makes a fair comparison impossible. 

Performance of M-168 (T-91-E1 ) . This was 
a late model fuze, and no more need be said 
here about its performance other than that it 


398 


ANALYSIS OF PERFORMANCE 


leaves little to be desired. Overall performance 
(lot groups 14 and 15) is as follows. 


Proper 
Late 
Early- 
Dud 

Number tested, 459 
Mean burst height, 50 ft 


92 per cent 

0 per cent 
7 per cent 

1 per cent 


Performance of T-50-EU and T-90. The 
scores obtained with the various lot groups 
(16 through 21) in this series are fairly uni- 
form. The lower dud scores appearing in later 
production are probably due mainly to improve- 
ments in detonator contact springs. The excess 
in early functioning of group 20 as compared 
with groups 16 and 17 may be due in part to 
factory rejected and reworked assemblies from 
T-92 production that were absorbed into T-90 
production. Excess earlies in group 19 are not 
so significant because this is a relatively small 
group. The variations in early and dud scores 
happen to be of a compensating nature, so that 
the proper function scores are quite uniform. 


Proper 

Late 

Early 

Dud 

Number tested, 2,153 


77 per cent 
1 per cent 
19 per cent 
3 per cent 


Of the approximately 130 metal parts lots of 
these fuzes, only 3 per cent were rejected. 

As in the case of Philco T-91, there appears 
with these fuzes a difference between mean 
burst heights of lot groups that cannot be ac- 
counted for quantitatively. The difference is 
about 10 ft (see groups 16, 17, and 18). There 
was an upward trend in carrier frequency, to 
the extent of about 1 me through part of the 
production represented by groups 16 and 17, 
but both theory and correlation tests using 
field data indicate that this could account for 
no more than 2.5 ft. As in the case of T-91, the 
difference is probably due to a combination of 
factors, and no rejections are desirable in esti- 
mating the overall average burst height, which 
is 39 ft. 

Performance of T-92 and T -9 2-El. The T-92 
is the only production fuze that exhibited gen- 
erally unsatisfactory scoring performance. The 
initial performance did not appear to be too 
bad, and it is suspected that a certain change 


in the fins of the test bombs (see “Effect of Re- 
lease Conditions” in this section) may have had 
something to do with the deterioration in per- 
formance. This does not appear to provide a 
full explanation ; a more basic explanation con- 
cerns an unusual dependence (at White fre- 
quency on the M-64) on the electric resistance 
between the bomb and its fin (see Section 
2.13.2). The broader pass band of the T-92 
amplifier made the effect more critical than in 
the T-50-E4. Quality of parts and workman- 
ship were apparently not at fault. Overall per- 
formance was as follows: 

Proper 57 per cent 

Late 1 per cent 

Early 34 per cent 

Dud 8 per cent 

Number tested, 1,034 
Mean burst height, 33 ft 

Of the 45 metal parts lots produced of the T-92, 
over 60 per cent were rejected. 

Only a few lots of the T-92-E1 were produced 
before the end of hostilities. Overall perform- 
ance was as follows : 

Proper 79 per cent 

Late 0 per cent 

Early 18 per cent 

Dud 3 per cent 

Number tested, 102 
Mean burst height, 40 ft 

Burst Height Distribution Characteristics. 
For a given type of fuze the spread in burst 
heights increases approximately in proportion 
to the mean burst height when the latter is in- 
creased by a change in such factors as reflection 
coefficient, altitude of release or plane speed. 
The evidence on this subject is summarized in 
“Burst Heights under Other Conditions” later 
in this section. 

The general character of the distribution of 
bursts obtained under supposedly constant 
testing conditions is shown for three fuzes in 
Figures 12, 13, and 14. The lot group numbers 
of Table 25 are given to identify the sources 
of data. The largest lot groups are used, with- 
out regard to target factor. It will be noted 
that the distributions are much the same in 
general character for all three fuzes. For some 
purposes the cumulative distribution curves 
(Figures 15, 16, and 17) are more useful. For 
practical purposes, these distributions may be 




SECRET 


BOMB FUZES 


399 


assumed to be linear when the cumulative per- 
centage is plotted on a probability scale and 
the burst height on a logarithmic scale. On 



Figure 12. Distribution of burst heights of 
Philco T-50-E1 fuzes over water (lot group 1). 

account of the approximately constant propor- 
tionality between the spread and the mean 
burst height, this type of distribution curve is 



Figure 13. Distribution of burst heights of 
Philco T-91 fuzes over land (lot group 8). 

simply displaced without change in slope when 
conditions alter the mean burst height. For a 
detailed study of distribution characteristics, 
see reference 35. 


Summary. The overall estimates of perform- 
ance derived above are summarized in Table 
27 for those fuzes that gave reasonably uni- 



Figure 14. Distribution of burst heights of 
Emerson T-50-E4 fuzes over water (lot group 
20 ). 


form and satisfactory performance. Excluded 
from the table are the first 42 metal parts lots 
of T-50-E1 that gave a high incidence of duds, 
and the whole of the T-92 production which 



Figure 15. Cumulative distribution of burst 
heights of Philco T-50-E1 fuzes over water (lot 
group 1). 


was rather uniformly unsatisfactory on ac- 
count of early functioning. Almost no T-92 
metal parts were loaded into ammunition lots. 


400 


ANALYSIS OF PERFORMANCE 


In comparing the performance of Brown and 
of White carrier fuzes it is apparent that the 
proper functioning performance of the Brown 
class is distinctly better than that of the White 
class, mainly on account of a lower incidence of 


Scores under Other Conditions 

Uniformity of Performance on Various Ve- 
hicles. Although the effect of vehicle size upon 
performance may be quite marked for fuzes of 
the ring type (if detuning occurs), observed 


Table 27. Summary of metal parts acceptance test performance. (Burst heights are for a water target of 
reflection coefficient 0.81 and a plane speed at release of 200 mph.) 


Fuze 

Make 

No. 

tested 

P 

Per cent scores 

L E 

D 

Mean burst 
height (ft) 



Brown carrier fuzes 





T-50-E1 

Philco 







and T-89 

and Simplex 

1,278 

83 

0 

13 

4 

35 

T-91 

Philco 

963 

87 

0 

11 

2 

37 


GE 

917 

84 

0 

10 

6 

44 


both 

1,880 

86 

0 

10 

4 

40 

T-91-E1 

Emerson 

459 

92 

0 

7 

1 

50 



White carrier fuzes 





T-50-E4 








and T-90 

Emerson 

2,153 

77 

1 

19 

3 

39 

T-92-E1 

Emerson 

102 

79 

0 

18 

3 

40 


early functions. This difference would be much 
more marked if the T-92 were included. On the 
other hand the overall incidence of duds, 4 per 



Figure 16. Cumulative distribution of burst 
heights of Philco T-91 fuzes over land (lot group 
8 ). 


cent, is slightly higher for the Brown carrier 
fuzes, and would be still higher if the first 42 
lots of T-50-E1 were included in the comparison. 


performance of the T-91 shows very good con- 
sistency for several different bomb sizes, as 
shown in Table 28. There is an apparent im- 



Figure 17. Cumulative distribution of burst 
heights of Emerson T-50-E4 fuzes over water 
(lot group 20). 


provement in performance on the M-64 bomb 
but the size of the sample is too small to give 
the trend real statistical significance. 



BOMB FUZES 


401 


Table 28. T-91 fuzes, performance versus vehicle 

(from 10,000 ft at 200 mph).* 


Vehicle 

Pw 

Per cent 

L E 

D 

Total 
No. of 
units 

M-30 

80 

0 

17 

3 

36 

M-57 

71 

0 

17 

12 

24 

M-88, -81 

81 

0 

12 

7 

798 

M-64 

89 

0 

7 

4 

98 


* Reference 66, acceptance tests. 


Effect of Release Conditions. (1) Altitude. 
In Table 29 are listed scores as a function of 
altitude of release, without regard to plane 
speed. A previous examination of the data had 
shown the latter to have no appreciable effect 
upon performance. It will be noted that results 
are fairly uniform (with one exception) with a 
tendency toward slightly poorer scores for high- 
altitude releases. The exceptionally high early- 
function scores for the T-92 units from 10,000 
and 20,000 ft should be considered in the light 
of the discussion in preceding section under 
“Performance of T-92 and T-92-E1” (pertain- 
ing to the data in Table 25) . 

2. Train spacing. The dependence of per- 
formance in train release upon the spacing of 
bombs is influenced by size of the bomb and 
the use of the delayed arming device. In Table 
30 are listed separately results without delays 
and those with delays. As may be seen, there 
is no indication of serious effect of train release 
upon dud score, and the effect upon early func- 
tioning decreases as the train spacing increases. 

The effect of spacing along with that of the 
arming delay may best be seen in Figure 18, 
where the per cent of early functions which oc- 
curred sympathetically f is plotted against inter- 
val between bombs at release. 

Because the data are meager, the random 
variations in results mask to some extent the 
real effects of the delays and of bomb size as 
shown in results of the bar-type fuze. There the 

f Early functions which were judged to have been 
caused by malfunctioning of neighboring units were 
called “sympathetic” functions. For the purposes of 
scoring, where photographic data were not available, 
functions within 0.5 sec or less of the original function 
were scored as sympathetic. Photographic evidence 
showed that for the most part, these functions occurred 
nearly simultaneously. 


evidence is strong that arming delays cut down 
appreciably the sympathetic functioning and 
that as the spacing increases, the sympathetic 
functions decrease rapidly. 

In Table 30, “int’l” stands for “intentional 
early.” In many train drops, one or more units 
were set to function on arming, at times later 
than normal arming time. This insured the oc- 
currence of one or more early functions in order 
to test the possible response of the other 
armed fuzes in the train to it. In the table, 
“sym” means sympathetic function; (Sym X 
100) /E is the percentage of earlies functioning 
sympathetically as plotted in the accompanying 
figure. 

Oddments. (1) Washers: Hand versus wrench 
tightening 18 During early testing of bomb fuzes, 
the general practice became established of 
mounting units to bombs using a % 2 -in- lock 
washer and tightening with a wrench. When it 
became apparent that the elimination of the 
wrench would be desirable, a new-type spring 
washer was introduced and the units were 
tightened by hand only. This method of mount- 
ing proved to be satisfactory for use with both 
the ring-type and the bar-type fuzes. 

A representative score of 83 per cent proper 
for T-91 fuzes released under standard condi- 
tions was obtained using this method. 

2. Navy base plates. 18 In Naval aircraft 
launching operations, a fuze protective device 
was used, consisting of two parts: (1) a metal 
sleeve, which was released when the bomb was 
dropped, and (2) a cruciform plate 7 in. in di- 
ameter, which served to hold the sleeve in posi- 
tion. This plate remained between the bomb 
nose and lock washer throughout the entire 
flight. Tests were made to see what effect the 
plate had on fuze performance. The results 
follow : 


No. of 


Unit 

Vehicle 

Alt. 

Speed Pw L 

E 

D 

Total %Pw 

T-50-E4* 

M-64 

10K 

200 

6 0 

12 

0 

18 

33 

T-50-E4 

M-64 

10K 

200 

9 0 

3 

0 

12 

75 

T-91 

M-64 

10K 

200 

18 0 

0 

0 

18 100 


* There is no known explanation for the difference in performance 
in the two tests of T-50-E4 units. 


3. Army guide plates. 18 The performance of 
T-91 units, assembled on bombs with Air Corps 
arming-wire guide plates, was tested. No sig- 


402 


ANALYSIS OF PERFORMANCE 


nificant effect was found. The results are as 5. Fin insulators , 75 In an attempt to reduce 

follows: the effect of fin upon the incidence of early 

^ functions, tests were made with pressboard 

Unit Mfr. Vehicle Alt. Speed Pw L E D Total Pw insulating spacers inserted between the outer 

T-91 Philco M-88 10K 200 ll 0 1 0 12 92 rim of the fin and the bomb. Somewhat contra- 

T-91 Phllco M “ 64 10K 200 12 0 0 0 12 100 dictory results were obtained. In Table 32 are 

4. Fin thickness . 74 Sometime during the listed results for three types of units dropped 

spring of 1945, excessive early-function scores under comparable conditions on M-64 bombs, 

Table 29. Effect of release conditions (single release). 

Altitude 

(ft) 

Speed 

(mph) 

Pw 

Per cent 

L E 

D 

Total Biblio- 

No. of graphical 

units reference 

9K-10K* 

160-200 

Unit T-91 
71 

0 


17 

12 

Vehicle M-57 

24 67 

3K 

255 

83 

0 


0 

17 

12 

20K 

234-240 

Unit T-91 

89 

0 


11 

0 

Vehicle M-81 & M-88 

37 15, 68 acceptance tests 

12K 

200 

73 

0 


27 

0 

30 

10K 

200 

81 

0 


12 

7 

798 

6K 

200 

93 

0 


7 

0 

30 

3K 

200 

90 

0 


3 

7 

30 

9K-10K 

150-200 

Unit T-91 

89 

0 


7 

4 

Vehicle M-6U 

98 69 

3K 

255 

82 

0 


18 

0 

11 

20K-21K 

218-240 

Unit T-50-E4 
81 

0 


15 

4 

Vehicle M-81 & M-88 

48 70 

12K 

200 

86 

0 


14 

0 

22 

10K 

200 

72 

0 


24 

4 

67 

6K 

200 

95 

0 


5 

0 

22 

3K 

200 

100 

0 


0 

0 

22 

20K-22.5K 

210-240 

Unit T-50-EU 
64 

3 


33 

0 

Vehicle M-6U 

36 

15K 

200 

92 

0 


8 

0 

12 71 acceptance tests 

10K 

200 

76 

1 


18 

5 

1,131 

7.5K 

200 

78 

0 


17 

6 

18 

5K 

200 

94 

0 


6 

0 

18 

20K 

240 

Unit T-92 

55 

0 


35 

10 

Vehicle M-6U 

20 15, 72 acceptance tests 

10K 

200 

58 

1 


34 

8 

1,246 

5K 

200 

85 

0 


15 

0 

20 

2.5K 

200 

85 

0 


15 

0 

20 


* K represents 1,000-ft units of altitude. 


were obtained in tests of White-frequency units 
mounted on M-64 bombs. It was found that the 
metal of the fins on these bombs was thinner 
than the usual 0.081-in. material. Tests con- 
ducted with M-64 bombs having fins of various 
thickness gave the results in Table 81. 

The above results with the 0.081-in. fin are 
in agreement with acceptance results of the 
same unit, i.e., 57 per cent proper for 1,000 
units. Acceptance tests were made on the M-64 
having nominal fin thickness of 0.081 in. 


both with and without the insulators. The dif- 
ference in scores for the T-92 units (disregard- 
ing duds) could occur fortuitously one or two 
times in a hundred. However, the scores for the 
T-92-E1 and T-50-E4 units show no statistically 
significant differences. 

6. Delayed arming device . 7(5 The delayed arm- 
ing mechanisms were designed as safety de- 
vices and as a means of improving performance 
of fuzes dropped from high altitudes. The de- 
vices have been tested primarily to obtain air- 



BOMB FUZES 


403 


travel data; a few were tested for performance, (from inexactitudes of both electric character- 

The scores of the latter tests follow. istics and conditions of release). 36 In addition, 

% % mean observed burst heights from actual field 

Unit Vehicle Alt. Speed Pw L E D N Pw E testing 15 ’ 78 have been spotted in with brackets 

T-50-E4 M-64 20K 240 14 0 4 0 18 78 22 indiratine- the standard error of the mean (+1 

T-50-E1 M-81 20K 235 19 0 3 0 22 86 14 bleating the standard error ol the mean < ±l 

T-91 M-81 20K 234 5 0 0 0 5 100 0 standard deviation) and the number of rounds 

Table 30. Performance in train, 73 HE-loaded bombs, ring-type fuzes (from 10,000 ft at 200 mph.) 



No. of 

No. of 

Early 

No. of 

Sym X 100 

Unit 

Vehicle 

trains 

units Proper Low 

Int’l 

Other 

Dud 

Sym 

E 




Without DAD * 









Interval: 15 ft 






T-50-E10 

M-81 

3 

29f 19 0 

5 

3 

0 

3 

38 

T-50-E1 

M-64 

2 

12$ 8 0 

0 

3 

0 

1 

33 




Interval: 50 ft 






T-50-E10 

M-81 

5 

48$ 33 0 

6 

8 

0 

1 

7 

T-50-E4 

M-64 

3 

18 6 0 

3 

9 

0 

4 

33 




Interval: 100 ft 






T-50-E10 

M-81 

2 

24 18 0 

4 

1 

1 

0 

0 




With DAD 









Interval: 15 ft 






T-91 

M-81 

3 

35§ 13 0 

6 

11 

0 

6 

35 

T-50-E1 

M-64 

2 

12 10 0 

0 

2 

0 

0 

0 




Interval: 50 ft 






T-91 

M-81 

3 

36f 24 0 

6 

4 

0 

2 

20 

T-91 

M-64 

2 

12 9 0 

2 

0 

1 

0 

0 

T-91 

M-65 

3 

6 10 

3 

2 

0 

1 

20 




Interval: 100 ft 






T-91 

M-64 

3 

18 14 0 

3 

1 

0 

0 

0 

T-91 

M-65 

3 

6 10 

3 

2 

0 

2 

40 




Interval: 150 ft 






T-91 

M-65 

2 

4 0 0 

2 

2 

0 

1 

25 


* DAD = delayed arming device, 
t 2 unaccounted for. 
t 1 unaccounted for. 

§ 5 unaccounted for. 


Although these results indicate no appreci- 
able effect of the delay upon performance, it 
should be noted that train drops of T-51 units 
made at Eglin Field indicated marked reduction 
of earlies by the use of the delay. 

Burst Heights under Other Conditions 

Effect of Altitude. Predictions of burst 
heights for various ring-type fuzes as a func- 
tion of release altitude for level flight at 200 
mph have been made using the method described 
in reference 25 and laboratory data given in 
Chapter 5. In Figures 19, 20, 21, and 22, pre- 
dicted heights are represented by solid lines; 
the dotted lines represent an appraisal of the 
cumulative error involved in the calculations 


upon which the means are based. Figure 23 is a 
plot of mean observed heights (photographic) 


Table 31. Effect of fins on performance.* 


Unit 

Pw L 

E D Total 

%Pw 

%E 


Fin-metal thickness: 0.073 in. 


T-92 

33 0 

34 5 72 

46 

47 

T-92-RGD 

8 0 

10 0 18 

44 

56 

T-50-E4 

8 0 

9 1 18 

44 

50 


Fin-metal thickness: 0.081 

in. 


T-92 

42 0 

23 6 71 

58 

32 


Fin-metal thickness: 0.105 

in. 


T-92-RGD 

14 0 

2 2 18 

78 

11 

T-50-E4 

24 0 

6 0 30 

80 

20 


* All rounds were dropped from 10,000 ft at 200 mph. The 
difference between the performances with the 0.073- and 0.105-in. 
fins is highly significant statistically. 


SECRF/lf 


404 


ANALYSIS OF PERFORMANCE 


versus predicted heights for these tests plus a 
number of earlier tests in which various experi- 
mental model fuzes were involved. 77 Each mean 
was obtained from a single test. 


Table 32. Effect of fin insulators on performance. 


Unit 

Insulator 

Pw 

L 

E 

D 

Total 

% 

Pw 

% 

E 

T-92 

Used 

32 

0 

6 

3 

41 

78 

15 

T-92 

Not used 

570 

100 

34 

8 

1,000 

57 

34 

T-92-E1 

Used 

17 

0 

0 

1 

18 

94 

0 

T-92-E1 

Not used 

13 

0 

3 

1 

17 

76 

18 

T-50-E4 

Used 

35 

1 

11 

1 

48 

73 

23 

T-50-E4 

Not used 

738 

10 

163 

48 

959 

77 

17 


It may be seen that despite rather large dis- 
crepancies in some cases between observed and 
predicted heights, for practical purposes the 
agreement is satisfactory. 

Effect of Vehicle. The design of the ring- type 
fuze is such that height of burst is affected by 
the bomb with which the fuze is used. In Table 
33 are given mean observed heights h for vari- 
ous fuze-missile combinations dropped under 
standard conditions (from 10,000 ft at 200 
mph) along with an estimated standard error 
of the mean S- h . For comparison are listed also 
heights for the given combinations predicted by 
the method outlined in reference 25 using lab- 
oratory data given in Chapter 5. Agreement be- 
tween the two values of heights is satisfactory 
if allowance is made for a possible 15 per cent 
error in prediction, as estimated on the basis of 
reasonable discrepancies in laboratory data and 
conditions of release. 30 

Table 33. Effect of vehicles on function height, 
ring-type fuzes (from 10,000 ft at 200 mph). 


Unit 

Mfr. 

Predicted 
height h 

Vehicle (ft) (ft) 


s- 

(ft) 

T-50-E1 

Philco 

M-81, M-88 

34 

32 


0.5 

T-50-E1 

GE 

M-81, M-88 

41 

43 

± 

3.2 

T-50-E4 

Emerson 

M-64 

49 

43 

Hh 

0.7 

T-91 

Philco 

M-30 

26 

28 


2.3 

T-91 

Philco 

M-81, M-88 

28 

29 

Hh 

0.9 

T-91 

Philco 

M-64 

18 

22 

± 

1.1 

T-91 

GE 

M-57 

35 

45 


4.9 

T-91 

GE 

M-81, M-88 

34 

41 


0.9 

T-92 

Emerson 

M-64 

42 

34 

± 

0.6 


References 15 and 79, acceptance tests. 


Effect of Train Release. Visual and photo- 
graphic observations indicate that when fuzes 
are dropped in train, a certain number of func- 
tions within the proper range are due, at least 
in part, to the functioning of neighboring fuzes. 
This is evidenced by an occasional stacking up 
of bursts with successive fuzes functioning at 
increasing heights. The effect of this sympa- 



TRAIN INTERVAL (FT) 



40 


30 

20 


1_J I I I I I I I I 1 ■! I 1 -1 


0 10 20 30 

40 50 60 70 80 90 100 IIO 120 130 140 150 160 17 

TRAIN INTERVAL (FT) 

Code 

Fuze 

o 

T-50-E10 

X 

T-50-E4 

□ 

E-50-E1 

■ 

T-50-E1 with arming delay 

▲ 

T-91 with arming delay 

Figure 18. 

Effect of train spacing and of arm- 


ing delay upon sympathetic functioning of ring- 
type bomb fuzes on HE loaded M-81, M-64, and 
M-65 bombs. 


thetic functioning among bursts within the 
proper range would be expected, on the whole, 
to raise the mean height of function. 

From the data tabulated in Table 34, there 
appears to be no dependence of burst height on 
this effect. It appears either that sympathetic 
functioning occurs less often than suspected 




ECRET 


BOMB FUZES 


405 


from visual observation 8 or that tolerances al- 
lowed in the manufacture of fuzes permits 
variation in burst height sufficient to partially 
mask the effect. This is further borne out by a 
Navy test of T-91 fuzes, released in train in a 
dive of 30 to 45 degrees (at 250 mph) , in which 
with intervals at release of 90 ft the rounds 



height of T-89. Vertical bar covers ±1 standard 
error of mean. 

scored as sympathetic propers in one train 
occurred higher than the regular propers and 
in another train lower. 


Table 34. Effect of train interval on function height, 80 
HE trains, ring- type fuzes.* 



Fuze: T- 

50-E4 

T-50-E10 


T-91 

T 

’-91 

Train 

Bomb : M-64 

M-81 

M-81 

M-64 

interval 

h 

Si 

h 

Si 

h 

Si 

h 

Sh 

(ft) 

(ft) 

(ft) 

(ft) 

(ft) 

(ft) (ft) 

(ft) 

(ft) 

15 



56 

±6.4 

31 

±3.0 



50 

30 

±3.5 

41 

±3.1 

34 

±3.4 

28 

±3.3 

100 



36 

±4.3 



23 

±3.0 

00 

43 

±0.07 



29 

±0.87 

22 

±1.1 


* The term h = mean burst height. The term = estimated standard 
deviation. Heights for single release drops are based on data for inert 
fuzes. 


Spread in Burst Height as a Function of 
Mean Burst Height. In Figure 24 are plotted 
values of standard deviation of burst height as 
a function of the mean burst height. Each point 
(except a few which cover acceptance testing 
of particular fuzes) represents the results of 

£ Studies have been made of photographic data to 
determine actual spacing between bursts which from 
one location appear to be sympathetic functions. It was 
found that in many instances these spacings were of 
such magnitude as to preclude the possibility of inter- 
action. 


an individual test of ring-type fuzes (involving 
on the average about 10 units). The line shown 
was determined by the method of least squares. 

Although inspection shows that some points 
fall far from the line, a general trend is defi- 



Figure 20. Effect of release altitude on burst 
height of T-90. Vertical bar covers ±1 standard 
error of mean. 


nitely indicated. For the purposes of rough 
estimates of burst height spread, a measure of 
this trend has been found useful. As determined 
from the slope of the straight line, the standard 
deviation is about 0.4 times the mean height. 34 



Figure 21. Effect of release altitude on burst 
height of T-91. Vertical bar covers ±1 standard 
error of mean. 


9 4 4 Bar-Type Fuzes 

Performance under Acceptance 
Test Conditions 

General Remarks and Lot Group Data. To the 
statements made in the first three paragraphs 
of Section 9.4.3 concerning the acceptance test- 




406 


ANALYSIS OF PERFORMANCE 


in g of and presentation of data on ring-type 
fuzes nothing need be added for bar-type fuzes 
except the information that the test vehicle was 
the M-81 (260-lb) fragmentation bomb. The lot 
group data are given in Table 35 and the group 
composition in Table 36. 



height of T-92. Vertical bar covers ±1 standard 
error of mean. 

Effect of Test Conditions on Performance. 
The theory of operation of bar-type fuzes pre- 
dicts that under the conditions of these tests the 


garded in estimating overall burst-height per- 
formance. 

There is no reason to expect the scores to be 
affected by either plane speed or target factor 
within the range of the test conditions. It could 
be shown from an analysis of lot-to-lot per- 



Figure 23. Observed versus predicted burst 
heights, ring-type bomb fuzes. Each point repre- 
sents one test. Line is the least-squares straight 
line of best fit. 

formance within groups 1 and 7 that there was 
a general downward trend in early functioning 


Table 35. Metal parts acceptance test results. 


Lot 

group 

No. 

Target 

factor 

Number 

units 

tested 

P 

Per cent score 
L E 

D 

Mean 

burst 

height 

(ft) 

Standard 

error 

mean 

(ft) 



T -51-El and T-51-E2 (Zenith) 




1 


590 

86 

1 

13 

0 

113 

1.0 

2 

65 

1,605 

91 

0 

9 

0 

88 

0.5 

3* 

60 

170 

92 

0 

8 

0 

77 

1.4 

4 * 

65 

677 

91 

1 

8 

0 

85 

0.9 




M-166 (Zenith) 




5* 

60 

112 

93 

0 

7 

0 

74 

2.2 

6* 

65 

41 

98 

0 

2 

0 

84 

3.2 




M-166 (Emerson) 




7* 

65 

300 

81 

2 

17 

0 

81 

1.6 

8* 

55 

149 

87 

1 

12 

0 

70 

1.6 




T-712 (Zenith) 





9* 

65 

34 

100 

0 

0 

0 

50 

1.9 


* Indicates 240-mph nominal true airspeed at release. 


effect of changes in plane speed on burst height 
would be of the same order as the tabulated 
standard errors of the means. Nothing in the 
data is to the contrary and this factor is disre- 


during the early production periods involved. 
The relatively high early-function scores of 
these groups thus happen to be associated with 
•higher target factors than the next lot group 



BOMB FUZES 


407 


in each case. Target factors, plane speeds, and 
the trends just mentioned are all disregarded 
in calculating overall performance. 

In contrast to the case with the ring-type 
fuzes, the mean burst heights of the bar-type 
lot groups are closely associated with the values 
of target factor, but the relation does not ap- 



Code Fuze 

O T -50-El, T-50-E4 

X T-91, T-91-E1 

A T-92 

Figure 24. Standard deviation versus mean 
burst height, ring-type bomb fuzes. Each point 
represents one test. 

pear to be one of strict proportionality. The 
burst height does not appear to change quite as 
rapidly as the target factor. A small and some- 



Figure 25. Distribution of burst heights of 
Zenith T-51-E1 fuzes over land (lot group 2). 


what arbitrary allowance for this situation is 
made in adjusting the group burst heights to 
a common target factor of 81. 

Burst Height Distribution Characteristics. 
The comments made in Section 9.4.3 on “Burst 


Height Distribution Characteristics” apply 
equally well to bar-type fuzes. Evidence on the 
relation between spread and mean burst height 
of bar-type fuzes is given in the following para- 
graph. The ratio of spread to mean is in gen- 
eral smaller for bar-type than for ring-type 


Table 36. Group identification for Table 35. 
(Duplication in lot number indicates part of the lot 
was tested under conditions of the particular group 
number.) 


Group 

number Metal parts lots 

1 CHU 1 through 50, 70 

2 CHU 51 through 119, 121 through 158 

3 CHU 194 through 198, 205, 206, 227, 228, 230 

4 CHU 158 through 191, 199 through 204 

5 CHU 5002, 5003, 5005 through 5009 

6 CHU 5001, 5004 

7 CEX 5001 through 5010, 5014 through 5018 

8 CEX 5011 through 5013, 5019 through 5023 

9 CHU 192, 193 


fuzes, and the distribution curve (see Figure 
25) is more symmetrical. A cumulative distri- 
bution curve is given in Figure 26. 



Figure 26. Cumulative distribution of burst 
heights of Zenith T-51-E1 fuzes over land (lot 
group 2). 


Summary of Performance. Apart from the 
variations mentioned in the preceding para- 
graph “Effect of Test Conditions on Perform- 


408 


ANALYSIS OF PERFORMANCE 


ance,” the performance of the lot groups of 
each manufacturer is very uniform. The overall 
results are given in Table 37. The proper func- 
tioning performance of the Zenith product is 
higher than that of Emerson, mainly on ac- 
count of the difference in early functioning. It 
is reasonable to assume that if the Emerson 
production had continued for a longer period, 
lower early function scores would have been 
obtained. 

No metal parts lots of bar-type fuzes were 
rejected. 

Table 37. Summary of metal parts acceptance 
test performance. (Burst heights are for a water 
target of reflection coefficient 0.81.) 

Mean 

burst 

Number Per cent scores height 
Fuze Make tested P L E D (ft) 


T-51-E1, 

T-51-E1, 

M-166 

Zenith 

3,195 

90 

1 9 <1 

110 

M-166 

Emerson 

449 

83 

2 15 <1 

110 


Scores under Other Conditions 

Uniformity of Performance on Various 
Vehicles. The design of the bar-type fuze is 
such that performance should be relatively in- 
dependent of the size of vehicle used. The field 
test results on inert-loaded vehicles, listed in 
Table 38, show no statistically significant dif- 
ferences in scores. There is a suggestion of 
somewhat impaired performance for the T-82 
on M-57. However, in the absence of any 
known physical basis for poorer performance 
on this bomb, it appears that the lower score 
should be attributed merely to sampling fluctu- 
ations. In any event, the effect is not serious. 
Numerous tests were made also of T-51 on 
other miscellaneous missiles (fire bombs, chem- 
ical bombs, etc.) and uniformly good perform- 
ance was obtained. Table 39, giving scores from 
the Eglin Field service test of T-51 units on 
HE-loaded vehicles, 49 indicates further the con- 
sistency of performance from vehicle to vehicle 
as well as that between inert- and HE-loaded 
rounds. 

Effect of Release Conditions. In Tables 40 
and 41 are listed results of single drops as a 
function of release altitude for inert- and for 


He-loaded vehicles. In two cases only do the 
proper scores fall below the 80 per cent mark ; 
both of these are for releases from 30,000 ft. 


Table 38. 
loaded. 

Performance versus 

vehicle, 

inert- 

Vehicle 

Per cent 

Piv L E 

D 

Total 

No. 


T-82 fuze, released from 10,000 ft at 200 mph* 


M-30 

97 

0 

3 

0 

30 

M-57 

68 

0 

25 

7 

28 

M-88 ) 

M-81 S 

83 

0 

11 

6 

480 

M-64 

73 

1 

19 

7 

70 

M-65 

88 

0 

12 

0 

16 

M-66 

100 

0 

0 

0 

10 

M-56 

100 

0 

0 

0 

4 

T-51 fuze, 

released from 

10,000 ft at 200 mph* 

M-57 

83 

0 

16 

1 

522 

M-88 ( 

M-81 S 

87 

1 

13 

0 

877 

M-64 

93 

0 

7 

0 

30 

M-56f 

100 

0 

0 

0 

14 

M-56$ 

100 

0 

0 

0 

14 


* Reference 81, acceptance tests. 

t These tests of T-51 on M-56 were made from various release 
altitudes (6,000 to 10,000 ft) and over various targets at Aberdeen 
and Eglin Field. 

t This group represents T-51 fuzes with reduced sensitivity (about 
|One-half normal) prepared specifically for use on M-56. The average 
burst height was 74 ft over the water target at Aberdeen. The 
reduced sensitivity fuze later carried the designation T-712. 


Table 39. Performance versus vehicle, HE-loaded. 


Vehicle 

Pw 

Per cent 

L E 

D 

Total 

No. 

T-51 fuze, released from 

10,000 ft at 225 mph 

M-30 

100 

0 

0 

0 

10 

M-81 

80 

0 

20 

0 

10 

M-64 

90 

0 

10 

0 

10 

T-51 fuze, released from 10,000 ft at 175 mph 

M-30 

80 

0 

20 

0 

10 

M-81 

80 

0 

20 

0 

10 

M-64 

80 

0 

20 

0 

10 


The remaining scores are consistently high and 
indicate little dependence of performance upon 
altitude of release. 

Performance in Train Release, with Special 
Reference to the Effect of the Arming Delay 
Device. The effect of train release upon the 
performance of bar-type fuzes is similar to that 
found with the ring-type fuze. Dud scores are 
affected but little, while early functioning is in- 
creased as train intervals decrease. 

Variations in score with bomb size and with 



BOMB FUZES 


409 


use of arming delays may be seen in Table 42. 
The graph in Figure 27 shows how the use of 
delays and increased spacing cut down sympa- 
thetic early functioning. 


Table 40. Effect of release conditions (single re- 
lease), bar-type fuzes, inert bombs. 


Altitude 

(ft) 

Speed 

(mph) 

Pw 

Per cent 
L E 

D 

Total 

No. 

T-82 Fuzes 82 

Vehicle: 

M-88 and M-81 


22.5K*-25K 

235-250 

80 

3 

17 

0 

36 

10K 

200 

83 

0 

11 

6 

480 

5K 

200 

80 

0 

20 

0 

10 

3K 

200 

86 

0 

0 

14 

42 

T-51 Fuze 88 1 

Vehicle: 

M-88 and M-81 


24K-25K 

225-250 

81 

2 

17 

0 

94 

20K 

210-250 

92 

0 

6 

2 

48 

10K 

200 

87 

1 

13 

0 

877 

3K 

255 

95 

0 

5 

0 

20 


T-51 Fuze 84 Vehicle : 

M-6U 



10K 

200 

93 

0 

7 

0 

30 

3K 

255 

100 

0 

0 

0 

12 


* K denotes altitude in thousands of feet, 
t Includes acceptance test results. 


Table 41. Effect of release conditions (single re- 
lease), bar-type fuzes, HE-loaded bombs. 49 


Altitude 

(ft) 

Speed 

(mph) 

Pw 

Per cent 
L E 

D 

Total 

No. 


T-51 -El Fuze- 

* Vehicle 

: M- 

-30 


30Kf 

225-260 

65 

0 

35 

0 

20 

10K 

175-225 

90 

0 

10 

0 

20 

5K 

150-200 

85 

0 

10 

5 

20 


T-51 -El Fuze 

Vehicle. 

: M-> 

SI 


30K 

230-270 

75 

0 

25 

0 

20 

10K 

175-225 

80 

0 

20 

0 

20 

5K 

150-200 

93 

0 

5 

2 

40 


T-51 -El Fuze 

Vehicle . 

: M - 1 

6A 


30K 

230-270 

80 

0 

20 

0 

20 

10K 

175-225 

85 

0 

15 

0 

20 

5K 

150-200 

95 

0 

0 

5 

20 


* Since a previous examination of the data had shown that the 
effect of the T-2-E1 device upon performance (in single release) was 
not appreciable, results with the delay were included in the tables 
above. 

t K denotes altitude in thousands of feet. 


The effectiveness of the arming delays in im- 
proving performance in train releases is out- 
standing. For example, in the worst possible 
cases, M-64 in salvo and minimum train, the 
use of the delays elevated the proper function 
score from 57 per cent to a level (86 per cent) 
that is almost identical with the performance 
of the fuzes in the metal parts acceptance tests 


(single release). The results indicate, there- 
fore, that the arming delays are highly effec- 
tive in eliminating sympathetic early function- 
ing. Indeed there is strong evidence that the 
proper use of arming delays obviates the need 
for certain limitations on train spacing that 
were considered to be of considerable impor- 
tance until these tests were performed. 

Oddments. 1 * (1) Washers, Hand versus 
Wrench Tightening. As with the ring-type fuze, 
the first established method of mounting bar- 
type fuzes to bombs was with a % 2 -in. lock 
washer and tightening with a wrench. The 



TRAIN INTERVAL (FT) 



Without 

With 

Bomb 

arming delay 

arming delay 

M-30 

o 

® 

M-81 

A 

▲ 

M-64 

□ 

a 


Figure 27. Effect of train spacing and of arm- 
ing delay upon sympathetic functioning of T-51 
fuze on HE loaded M-30, M-81, and M-64 bombs. 


effect upon performance of the use of a lock 
washer and tightening by hand only was tested. 
The following typical results show no indication 
of deterioration in performance when these 



410 


ANALYSIS OF PERFORMANCE 


fuzes are mounted hand-tight instead of wrench- No deterioration in performance had been 

tight. anticipated, and none was observed. 

gpeed 3. Delayed Arming Device. Except for train 

Alt. (mph) Vehicle Pw L E D N %Pw drops of T-51 units in the Eglin Field service 

T-51 Fuze test, only a few bar-type fuzes equipped with 

20K 240-250 M-88, -81 22 0 l 1 24 92 delayed arming mechanisms were tested for 

10K 200 M-88 30 0 0 0 30 100 normal approach function. The results are listed 

T - 82 Fuze below. 

10K 200 M-88 21 0 2 0 23 91 

Unit Vehicle Alt. Speed Pw L E D N fyPw %E 
2. Army Guide Plates. The performance of T _ 82 m- 81 10K 200 9 0 l 0 10 90 10 

T-51 units assembled on bombs with Air Corps T-51 M-81 10K 200 8 l l 0 10 80 10 

arming-wire guide plates, was tested. Twelve T " 51 M " 81 25K 22 °" 250 H 1 0 0 12 92 0 

rounds on M-88 from 10,000 ft at 200 mph gave These results are too meager to indicate 

100 per cent proper function. much improvement in performance. However, 

Table 42. Performance in train, 49 HE-loaded bombs,* T-51-E1 fuzes (from 10,000 ft at 200 mph). 


No. of 



No. of 

No. of 


No. of 

Sym X 100 

Vehicle 

trains 



fuzes 

P L 

E 

D 

Sym 

E 






With no ay'ming delay 

device 









Salvo 





M-30 

2 



48 

23 1 

24 

0 

17 

71 

M-81 

2 



44 

3 0 

37 

4 

35 

95 

M-64 

4 



48 

22 0 

26 

0 

20 

77 






Minimum train 





M-30 

2 



47 

38 0 

9 

0 

5 

56 

M-81 

2 



44 

38 2 

3 

1 

2 

67 

M-64 

4 



48 

27 0 

20 

It 

17 

85 






50- ft interval 





M-30 

2 



48 

37 0 

10 

1 

3 

30 

M-81 

2 



44 

40 2 

2 

0 

0 

0 

M-64 

2 



24 

22 1 

1 

0 

0 

0 






100- ft interval 





M-30 

2 



48 

44 0 

4 

0 

1 

25 

M-81 

2 



44 

37 0 

7 

0 

0 

0 

M-64 

2 



24 

22 0 

2 

0 

0 

0 





With T-2-E1 arming delay device 







Setting 

: 7 Div. on M-30, -81. 

6 Div. 

on M-61t 








Salvo 





M-30 

2 



48 

47 0 

1 

0 

0 

0 

M-81 

2 



44 

42 0 

2 

0 

0 

0 

M-64 

6 



58 

54 0 

4 

0 

2 

50 






Minimum train 





M-30 

2 



44 

39 0 

1 

4 

0 

0 

M-81 

2 



44 

40 1 

3 

0 

0 

0 

M-64 

5 



60 

48 0 

10 

n 

5 

50 






50-ft interval 





M-30 

2 



48 

45 0 

2 

i 

0 

0 

M-81 

2 



44 

39 0 

5 

0 

0 

0 

M-64 

4 



48 

42 1 

5 

0 

1 

20 






100- ft interval 





M-30 

2 



48 

39 0 

8 

1 

0 

0 

M-81 

2 



44 

43 0 

1 

0 

0 

9 

M-64 

2 



24 

20 1 

3 

0 

0 

0 


* Table combines trains dropped over water and land, 
t Low-order detonation. 
t One function on impact. 



BOMB FUZES 


411 


the drops in train at Eglin Field showed a 
marked reduction in early functioning by the 
use of the delay. 

Burst Heights under Other Conditions 

Effect of Altitude. Dependence of burst 
height upon altitude of release is shown in Fig- 
ure 28. Curves of heights predicted by the 
method given in reference 33 are shown. Mean 
burst heights from field testing have been 
spotted in along with an estimate of their 


dicated differences in fuze sensitivity, and 
when differences in release conditions obtained. 

Effect of Train Release. The possibility of 
sympathetic functioning for the ring-type fuzes 
in the region of proper burst heights has been 
discussed in Section 9.4.3. If sympathetic func- 
tioning did occur in the proper function zone, 
one would expect to find the burst height in- 
creasing with smaller train spacing. However, 
the mean burst heights of bombs fuzed with the 
T-51, as in the case of the ring-type fuzes, do 



Figure 28. Effect of release altitude on burst height of T-51 fuzes on M-30, M-81, and M-64 bombs. 


standard error and the number of units in- 
volved. It will be seen that if allowance is made 
for a discrepancy of about 10 per cent in pre- 
diction, the agreement between predicted and 
observed heights is reasonably good. 

Effect of Vehicle. The effect of vehicle on 
height of burst of bar-type fuzes is shown in 
the data tabulated below. Table 43 gives burst 
heights for single releases over water from 
10,000 ft at 200 mph. Table 44 gives the ratio 
of the burst heights for the fuzes on various 
bombs to those on the M-81. (Data are based on 
experimental field tests at Aberdeen, service 
tests at Eglin Field, and metal parts acceptance 
tests.) In deriving these ratios adjustments 
were made when laboratory measurements in- 

IH 


not appear to be affected by train spacing. The 
mean burst heights for several different bombs 
and for difference train releases are presented 
in Table 45. 

Spread in Burst Height as a Function of 
Mean Burst Height. A plot of spread in burst 
height (see Figure 29) as a function of mean 
burst height for the bar-type fuze shows much 
the same trend as that for the ring-type fuze 
(see Section 9.4.3). In Figure 29 the standard 
deviation from the mean is used as the measure 
of spread, each point representing the results 
of one test. Although the scatter from the line, 
which was determined by the method of least 
squares, is in some cases quite marked, for 
practical purposes a measure of the trend has 

3 



412 ANALYSIS OF PERFORMANCE 




Table 43. ] 

Effect of vehicle on function height (bar- type fuzes). 



Fuze 

M-30 

h* Si f 

M-57 
h Si 

CQ 

t-h 00 

00 00 

'-ss 

M-64 
h Si 

M-65 
h Si 

M-66 
h Si 

M-56 
h Si 

T-51 

T-82 

142J =*= 14f 
107 ±4.6 

121 ±1.4 
111 ±5.9 

111 ±0.9 

120 ±1.4 

75 ±3.3 

99 ±4.5 

77 J ±8J 

57 ±3.5 

44 1 ±3t 

57 ±4.2 

1574 =*=12t 

67 ±7.7 


* h = mean burst height in feet. 

t Sfi = estimated standard error of the mean. Reference 85, acceptance tests. 

| These heights estimated from Table 44; no field data available for standard release conditions. 


Table 44. Ratio of burst heights of various bombs 
to burst height of M-81 with T-51 and T-82 fuzes. 86 


Bomb 

T-51 

T-82 

M-30 

1.28 ± 0.10 

0.94 ± 0.05 

M-57 

1.00 ± 0.05 

0.94 ± 0.06 

M-88 

1.00 ± 0.05 

1.00 ± 0.03 

M-17 

0.60 ± 0.07 


M-64 

0.73 ± 0.03 

0.86 ± 0.05 

M-65, -79 

0.69 ± 0.10 

0.50 ± 0.03 

M-66 

0.40 ± 0.06 

0.53 ± 0.04 

M-56 

1.37 ± 0.08 

0.49 ± 0.05 


was superimposed on the other to form a box 
1 ft deep. The bottoms consisted of %-in. ply- 
wood panels 6 ft long and 2 ft wide. Trenches 
were excavated 6 in. beneath the surface, the 
boxes inserted and leveled, and a sand parapet 
built around the upper 6-in. frame. The 
trenches were arranged in columns and rows, 
47 each, spaced 15 ft between centers. Odd- 
numbered columns had the long dimension of 
the trench in an east-west direction, while 


Table 45. Effect of train interval on burst height, 49 HE-loaded bombs fuzed T-51-E1. 



Type of 


Minimum 

50-ft 

100-ft 

100-ft train 

Bomb 

release 

Salvo 

train 

train 

train 

double susp. 



h* Si f 

h Si 

h Si 

h Si 

h Si 



(ft) 

(ft) 

(ft) 

(ft) 

(ft) 


M-30 

128 

±7 

121 

±5 

127 

±4 

142 

±5 

152 

±8 

M-81 

130 

±3 

108 

±3 

126 

±4 

145 

±6 



M-64 

60 

±5 

79 

±4 

80 

±3 

92 

±3 




* The term h = mean burst height (released over water, from 10,000 ft). 
fThe term Si = estimated standard error of the mean. 


been found useful. As determined from the 
slope of the line, the standard deviation is 
about 0.23 times the mean height. 34 


Effectiveness of Air Burst 

Enhanced Fragmentation Effect 

Against Moderately Shielded Personnel. Test- 
ing was done at Eglin Field to determine the 
relative effectiveness of air-burst and contact- 
burst bombs against moderately shielded per- 
sonnel (both T-50 and T-51 fuzes were used). 
Bombs were dropped over an effect field 
700x700 ft. The field contained 2,209 replica 
trenches, constructed as follows. The sides con- 
sisted of two rectangular frames 6 ft long and 
2 ft wide constructed of lx6-in. pine. One frame 


those in even-numbered columns had the long 
dimension in the north-south direction. 

In scoring the results, a casualty was defined 
as one or more “large” perforations through 
the wooden lining of a trench. In the classifi- 
cation of hits as “large” or “small,” a probe 
approximately %6 X %6 in* in cross-sectional 
area was used. Relatively few perforations 
were as small as this probe. Figures 30 and 31 
show results for single releases from 6,000 ft 
at 165 mph (chosen to give maximum accuracy 
of aim and at the same time give the same 
striking angle as a 10,000-ft, 200-mph release) 
of 19 M-81 bombs VT-fuzed, as follows: 14 
M-64 bombs VT-fuzed; 6 M-81 bombs contact- 
fuzed (instantaneous) ; 5 M-64 bombs contact- 
fuzed (instantaneous) for 3 degrees of shield- 
ing. Ten M-1A1 clusters of M-41 bombs, con- 
tact-fuzed (instantaneous), were included in 



BOMB FUZES 


413 


the test. Hits for the various degrees of shield- 
ing were included in the count, as follows. 

Shielding Hits Counted 

0 in. On sides and bottom 

6 in. On lower 6 in. of sides and bottom 

12 in. On bottom only 

No significantly differing results were ob- 
tained in additional releases from 12,000 and 
20,000 ft. 

In Section 9.2.3, attention was called to the 


Complete analysis and interpretation of the 
results is somewhat lengthy; reference may be 
made to the Army Air Forces Board report, 45 
where the following conclusion is drawn. 

“Under the conditions of this test and for 
equivalent airplane loads of properly function- 
ing bombs, air-burst M-81 or M-64 bombs are 
about ten times as effective in producing frag- 
ment casualties as are the same bombs or the 
20-lb M-41 fragmentation when contact-burst.’' 



Code Fuze 

A T-82, T-82-E1 

X T-51, T-51-E1 

Figure 29. Standard deviation versus mean burst height, bar-type bomb fuzes. Each point represents 
one test. 


significance of “zero shielding” in the assess- 
ment of results obtained on this effect field. 
From the foregoing description of the field, it is 
clear that, except for a bomb that strikes in- 
side a trench, a fragment cannot register a hit 
unless it is traveling in a downward direction 
from a level above that of a parapet tlrat sur- 
rounds a trench. Many of the fragments from 
a contact-fuzed bomb fail to satisfy this condi- 
tion. The results of the test are therefore not 
applicable to a case of troops lying exposed on 
a mathematically flat plane. The zero-shielding 
condition approximates more closely a case 
where troops are lying on a terrain with fre- 
quent irregularities of an average height or 
depth of about 6 in. 


Against Unshielded and Shielded Personnel 
and Against Unshielded Materiel. The British 
carried out an evaluation of air-burst bombs 
against a composite close support target. 87 
American fuzes (T-50 type) and bombs 
(M-64) were used. Division 4 cooperated in the 
tests, operating through the London branch of 
OSRD. 

The target consisted of unshielded trenches 
and simulated prone and entrenched personnel. 
About 200 trenches 2x6 ft and 1 ft deep were 
randomly located in an area about 500x1,000 ft. 
Centered in the bottom of each trench was a 
16 x 46 x 1 / 2 -im target board, simulating the vul- 
nerable area of either three men standing or 
crouching in a deep trench or one man lying in 


414 


ANALYSIS OF PERFORMANCE 


a shallow trench. Two boards (10x60xV2 in.) 
nailed together as an inverted trough were 
placed on the ground near each trench, simulat- 
ing prone soldiers on reasonably level ground. 
Thirty-six trenches were scattered at random 
in the center of the target area. One or more 
perforations through a board target counted 



Figure 30. Casualties as function of burst 
height of M-81 fragmentation bomb for several 
degrees of shielding. Vertical bar indicates ±1 
standard error of mean. 

as a casualty. In the case where the boards in 
trenches represented three men in a deep 
trench, the number of perforations were 
counted, and on a probability basis, scored as 
one, two, or three casualties. Boards destroyed 
by blast within 50 ft of the burst were scored 
as complete casualties. Trucks were carefully 
examined after each bomb burst and only those 
damaged to the extent that rear-echelon repair 
was necessary were counted as casualties. 

Results were expressed in terms of lethal 
areas. Comparison tests with contact-burst 
bombs were not made at the same time but pre- 
vious tests had established vulnerable areas for 
them under reasonably similar conditions. A 
summary of the results and comparison data 
are shown in Table 46. 

Against Unshielded Materiel and Deeply En- 
trenched Personnel. An extensive test to deter- 
mine the effectiveness of air-burst and contact- 
burst fragmentation and incendiary bombs 
against typical enemy defense fortifications 
was conducted at Eglin Field. 47 Because of the 
complexities involved in the analysis of the re- 
sults, details are herein omitted. 

From the analysis, it appeared that for 


totally unshielded trucks and light materiel, a 
plane load of air-burst bombs was about 80 
per cent as effective as one of contact-burst 
bombs. However, the advantage may be more 
apparent than real in view of the following 
considerations : 

1. When the results of the test were assessed, 
it was not known that double suspension of 
VT-fuzed M-30 and M-81 bombs was prac- 
ticable. Twenty-four M-30’s and 22 M-81’s were 
used as full VT-fuzed loads in B-17 bombers; 
it now appears that 34 bombs could have been 
carried without sacrificing good performance. 

2. The assessed effectiveness might be 
greater if account were taken of the likelihood 
that aircraft would be dispersed in revetments. 



Figure 31. Casualties as function of burst 
height of M-64 GP bomb for several degrees of 
shielding. Vertical bar indicates ±1 standard 
error of mean. 

As for deeply entrenched personnel (depth 
of shielding was 5 ft) , so slight was the dam- 
age done by either air or contact burst that no 
assessment of relative effectiveness could be 
made. 

Miscellaneous Eglin Field 
Testing of Effectiveness 

During the later stages of World War II, 
much interest developed in fire bombing with 
napalm-gasoline gel. Spectacular results were 



/ 


BOMB FUZES 


415 


obtained by dropping fuel tanks of this ma- 
terial from fighter planes flying at such a low 
altitude that the gel sloshed over a large area 
immediately after the tanks were ruptured by 
impact. Under conditions where low-level at- 
tack was too dangerous, high-altitude releases 
of contact-fuzed vehicles gave poor results be- 
cause a large fraction of the gel remained in 
the crater. A number of tests were performed 
with VT-fuzed vehicles to overcome this diffi- 
culty. In all cases, the performance of the VT 


the possible increased lethality of large blast 
bombs when air burst. Early in World War II 
the British prepared a number of special fuzes 
to provide air bursts on their 4,000-lb high- 
capacity [HC] bomb. Burst heights were set 
for around 200 ft, which was believed to be the 
optimum height of function. These bombs were 
dropped over enemy territory and the damage 
assessed by photographic coverage. The results 
showed a decrease in area of demolition and a 
small increase in area of minor blast damage 92 


Table 46. Advantage ratios in favor of 500-lb bombs fuzed T-50. 


Men 



Height 

Men in 

Men in 

prone 



of burst 

deep 

shallow 

without 

Mechanical 

Target 

(ft) 

trenches 

trenches 

cover 

transport 

Effectiveness relative to surface 

10 

4.0 

3.7 

1.3 

1.0 

bursts 

36 

3.7 

5.3 

1.2 

0.4 

Effectiveness relative to a 

10 

1.8 

1.2 

1.4 

1.6 

method yielding 50% air 

36 

1.7 

1.7 

1.3 

0.7 

bursts using 0.6-sec train 






spacing* 






Lethal or vulnerable areas (sq 

10 

5,200 

5,600 

25,000 

38,000 

ft) 

36 

4,800 

8,000 

24,000 

16,000 

* This method consisted of dropping 

a stick of four bombs fuzed with 

No. 44 pistol (a pressure-activated fuze). 

Usually two bombs of 

the train would function on impact and 

the other two 

would be air burst. 

actuated by the blast of 

the others. Tests with this arrangement 


had been performed previously. 

The British results were in substantial agreement with the Eglin Field results described when due allowances are made for the differences 
in scoring.88 The lower ratios of effectiveness reported by the British for air burst were due primarily to the allowances made for blast. This 
allowance increased appreciably the lethal area of the surface-burst bombs. 

Because of the minor differences in effectiveness against personnel for 10- and 36-ft burst heights and the appreciably greater effective- 
ness of the former against mechanical transport, the British prefer the lower burst heights. In their official requests for American fuzes for 
their operational use, they specified burst heights of the order of 10 ft. 


fuzes was satisfactory, and the main problem 
was to find a container that was available in 
large quantity in the theaters of operation that 
could readily be modified into a bomb having 
suitable bursting and ignition characteristics, 
suitable ballistic characteristics, and that could 
be carried economically by fighters or bombers. 
One improvisation was a modified chemical 
warfare M-10 (35-gal) spray tank, which gave 
rather satisfactory results when fuzed T-50- 
E4, or fuzed T-51-E1 in combination with a 
“slow” burster. 46 Considerable success was 
achieved in an extensive program for the de- 
velopment of a vehicle specifically designed for 
fire bombing, but this program was incomplete 
when terminated at the close of hostilities. 

Enhanced Blast Effect 

A number of experiments were performed 
both in America and in England to determine 


and, accordingly, interest in the air burst of 
large blast bombs diminished. Following these 
tests, work on the T-40 and T-43 fuze projects 
(see Chapter 1 and Section 3.5) was appre- 
ciably curtailed. 

However, Division 2, NDRC, and British ex- 
plosive experts were convinced that demolition 
from blast could be increased by air burst and 
set about to determine the optimum height. 
Extensive small-scale 89 and model-village tests 90 
showed conclusively that blast damage could be 
increased by air burst at the proper height. 
Optimum heights for a 4,000-lb bomb were esti- 
mated at between 40 and 70 ft. 91 Increases in 
area of demolition were estimated at from 50 to 
100 per cent. The conclusions were further cor- 
roborated by analysis of the areas of damage 
produced by a few V-l bombs which were acci- 
dentally air burst in the London area. 92 

No full-scale tests were carried out prior to 


416 


ANALYSIS OF PERFORMANCE 


the end of World War II to verify the above 
conclusions. However, as is shown in Table 38 
above, the T-51 fuze could be modified to oper- 
ate reliably on the M-56 (4,000-lb) bomb. The 
British also established that the T-51 fuze 
could be modified to operate reliably on their 
4,000-lb HC bomb. 93 

Enhanced Spread of Gas 

A number of tests were carried out to deter- 
mine the effectiveness of air-burst bombs in en- 
hancing the spread of mustard-type gas. These 
tests were made by the British in England and 
in Anglo-American tests in Panama in simu- 
lated jungle warfare. The T-51 and T-82 fuzes 
were used on British 500-lb light-case [LC] 
Mark II bombs. In this bomb, which contains 
two bursting elements, the proximity fuze was 
located in the nose and an impulse fuze was 
located in the tail. The actuation of the prox- 
imity fuze triggered the tail fuze so that both 
bursters were effective in dispersing the gas. 
The results of the tests in England have not 
been published but have been communicated 
verbally to Division 4. 94 The results showed 
that for a 50-ft average air-burst height, the 
area contaminated to the extent of 1 mg per 
sq m was approximately 4% times the area 
contaminated by the surface burst. For burst 
heights in the range 100 to 200 ft, the area con- 
taminated (again 1 mg per sq m) was approxi- 
mately seven times the corresponding area for 
surface-burst bombs. Publication of the British 
results was withheld pending an investigation 
of the inflammability of mustard gas when air 
burst. Subsequent tests at Panama 95 showed 
that mustard did not ignite when air burst. 

In the tests at Panama 96 ’ 97 in which the con- 
ditions of jungle warfare were simulated, it 
was desired to have the air burst just below the 
level of the treetops in order to contaminate the 
area under the canopy. It was found that full- 
sensitivity T-51 fuzes gave air bursts in the 
treetops or just above, but half-sensitivity T-51 
fuzes gave burst heights just below the treetop 
level and produced an optimum effect. Results 
from the Panama test were : 

1. Thirty bombs impacted on the target area 
produced an average contamination density of 
about 2 bombs (containing 350 lb of agent) per 


artillery square, or about 54 tons of agent per 
square mile. 

2. Vapor dosages greater than 200 mg-min 
per cu m were attained over about three-quar- 
ters of the target area within the first four 
hours after bombing. Dosages exceeding 1,000 
mg-min per cu m were obtained over about one- 
third of the area in this period. 

3. The half-sensitivity T-51 fuze was con- 
sidered a suitable and desirable fuze for the 
British bomb, aircraft LC 500-lb Mark II, 
charged with blister gas for use on jungle ter- 
rain. 

95 FUZES FOR MORTAR SHELLS 

951 General 

Since no VT fuzes for mortar shells reached 
the mass production stage, it is not possible to 
estimate the quality of performance that could 
have been attained with production fuzes. Ex- 
perience with all other VT fuzes showed that 
performance of mass production models was 
superior to that of experimental and pilot pro- 
duction models. There is no reason to suspect 
that experience with mortar-shell fuzes would 
have been otherwise. It is, therefore, believed 
that an average measure of the observed per- 
formance of the more recent developmental 
models may be fairly presented as a lower limit 
for the quality of performance that could be 
expected of production fuzes based on the de- 
velopment prior to V-J Day. 

The presentation of a lower limit for quality 
of performance is not very satisfactory in 
evaluating the potential usefulness of a devel- 
opment program, and the data are therefore 
presented very briefly. Specific test references 
are omitted. Coverage is defined by a statement 
of the characteristics of the tests performed 
during a certain period that are included in the 
analysis. The source material can be identified 
by reference to summaries of field test re- 
sults. 19 ’ 20 > 30 ’ 39 

• • 

95 2 Reliability and Burst Heights 
Globe-Union T-132 

Performance under Standard Conditions. A 



FUZES FOR MORTAR SHELLS 


417 


fairly large number of pilot production Globe- 
Union T-132’s were fired in what were called 
“lot quality tests/’ These were fired under 
somewhat similar conditions at Blossom Point 
and at Clinton Proving Ground. In the sum- 
mary in Table 47, the analysis is limited to 
those rounds fired on M-43C shells. 11 

As one would expect, the fuzes differed from 
lot to lot as test results indicated that changes 
were necessary. Variations among the units 
considered in this summary include the follow- 
ing: 

1. Amplifier plates: thin or thick horizontal 
plates. 

2. Turbine speed: high (most units) to low 
(half of high speed). 

3. Nose shape: flat (most units) and 
rounded. 

4. Thrust washers: vary in number from 
one to nine. 

5. Regulation circuit: series or parallel; 
light or heavy loading. 


grouping was necessary to consolidate the 
Blossom Point data with the results from Clin- 
ton Proving Ground where no distinction be- 
tween early and middle functions was made. 
A small fraction, about 4.3 per cent of the 
proper functions given above, was classed in 
earlier reports as impact functions. Because 
the average burst height was in the neighbor- 
hood of 10 ft, and because the principle of op- 
eration of the fuze makes it improbable for the 
fuze to function normally at more than three 
levels between 15 and 0 ft, some functions at 
water level were to be expected. Detonations 
initiated at the surface may yield bursts below 
the surface, on account of delay in the detona- 
tor and spotting charge. It is doubtful that any 
of these functions were actually caused by im- 
pact, through either mechanical or electric 
action. 

The poorer scores for firing with charge 4 
(Table 47) were being corrected by V-J Day 
by the use of slower turbine speeds, better 


Table 47. Summary of performance of Globe-Union T-132 for the months of June and July 1945 at Blossom 
Point and Clinton. 


Quadrant 

Charge elevation Per cent 

(M-56) (degrees) N P E D H (ft) N h * 


1 

65 

270 

75 

7 

18 

7 

184 

1 

75, 80 

221 

85 

9 

6 

8 

153 

2 

65 

196 

72 

13 

15 

7 

67 

3 

60, 65 

249 

71 

12 

17 

5 

24 

4 

45 

300 

60 

22 

18 

15 

68 

4 

65 

360 

57 

19 

24 

5 

150 

4 

75, 80 

94 

56 

37 

6 

9 

51 


Overall scores 

1,690 

68 

16 

17 

8 

697 


* Number of rounds upon which height is based. 


6. Arming: settings were changed occasion- 
ally but not enough to affect performance 
markedly. The above variations did not cause a 
statistically significant difference among the 
function scores, and should not affect the func- 
tion height. The absence of significant difference 
may be partly due to the small number tested 
with some variations, but there is no serious 
objection to pooling the data for the purpose of 
this summary. 

In Table 47, the early functions include those 
called middle functions at Blossom Point. This 

h The M-43C is a combination of the M-43 body and 
the M-56 tail. 


thrust washers, and vertical-plate amplifiers 
(see Chapter 4). These changes would reduce 
early function and dud scores by reducing 
breakage of the plates at high acceleration, 
erratic behavior of the mechanical system at 
high acceleration and speed, and explosion of 
rotors by centrifugal force. 

Performance after Packaging Tests. The 
only special test which is pertinent to the pres- 
ent discussion is that of performance after 
packaging tests at Picatinny. Twelve Globe- 
Union T-132 fuzes from lot GUS-17 were tested 
in the laboratory before and after being sub- 
jected to packaging tests at Picatinny. (The 


418 


ANALYSIS OF PERFORMANCE 


laboratory tests showed changes in electric 
characteristics which, in view of changes in 
control units from the same lot not subjected to 
the packaging tests, were considered caused by 
aging only.) The field test of these units gave 
the following results : 


Quadrant 



elevation 


Burst 

Charge (de- 

Num- 

Per cent height 

(M-56) grees) 

ber 

FED (ft) 

4 45 

12 

58 8 33 9 


This score is not significantly different from 
that in the summary above. 

National Bureau of Standards T-171 Fuze 

The National Bureau of Standards [NBS] 
T-171 fuze was used as an experimental unit, 
and many variations in electric and mechanical 
systems and in power supply were used. The 
summary in Table 48 includes only those units 
with RC arming. The other variations found 
among these units would be expected to affect 
function heights obtained with M-56 Ext. 1 shell 
so that no reliable figure may be given for 
overall performance in that respect. The aver- 
age function heights for various tests on this 
shell varied from 36 to 61 ft. The function 
scores and heights with the M-43C shell were 
not affected enough to prohibit pooling the re- 
sults. Firing conditions were limited almost 
exclusively to those listed in Table 48. 

There are no pertinent tests made with NBS 
T-171 which are not included in Table 48. 

Table 48. Performance of NBS T-171 from June 1 

to September 20, 1945. 


Quadrant 

elevation 


Charge 

Vehicle M-56 

(de- 

grees) 

N 

Per cent 
P E 

D 

H 

(ft) 

Nn 

M-43C 2 

45 

30 

77 

13 

10 

14 

0 

M-43C 4 

45 

139 

65 

13 

22 

20 

72 

M-56 Ext. 1 

45 

72 

61 

17 

22 



Overall score 

241 

65 

15 

20 




WURLITZER T-171 AND ZENITH T-172 FUZES 

Not enough rounds were fired with either of 
these fuzes to obtain any idea of their probable 
future performance. 

1 The M-56 shell with a 2-in. rearward displacement 
of the tail assembly, designed to stabilize flight of the 
VT-fuzed shell. 


Safety and Arming 
Globe-Union T-132 

General. No data are available on times or 
distances to complete arming of T-132 units. 
Summary data on mechanical arming are pre- 
sented below. The most reliable data are prob- 
ably the arming times, obtained either from 
fuzes modified to function on mechanical arm- 
ing [FOMA] or from fuzes so modified that the 
carrier signal was extinguished momentarily 
on carrier indication of mechanical arming 
fCIMA] (see Chapter 8). 

It should be noted that the arming times are 
approximately inversely proportional to the ve- 
locity during burning, so that the mechanical 
arming distance is nearly independent of the 
propellent charge. It follows from this that the 
round-to-round variations in velocity that oc- 
cur with a fixed charge are reflected in round- 
to-round variations of arming time. For this 
reason, it is to be expected that the propor- 
tional variation in arming time would exceed 
the proportional variation in arming distance. 
A detailed analysis of arming performance is 
not included here, since a major change in the 
arming mechanism was under development 
(see Chapter 4), and would undoubtedly have 
been used if the fuze had gone into produc- 
tion. 

Arming Data. (1) Arming times. Arming 
time of a FOMA unit was obtained by averaging 
values obtained by several field observers with 
stopwatches or by averaging the stopwatch 
times to the end of the phonograph recording of 
carrier modulation obtained by playing the 
record several times. Arming time of a CIMA 
unit was obtained by measurement of a photo- 
graphic record of carrier modulation or by 
averaging stopwatch times obtained by playing 
the phonograph recording of carrier modulation 
several times. These techniques are described 
fully in the preceding chapter. Results on arm- 
ing times are shown in Table 49. 

2. Arming distances. An attempt was made 
to measure the slant distance from firing point 
to function of 47 FOMA units. The work was 
complicated by photographic troubles and the 
results, shown in Table 50, may be in error by 
±50 ft. 


FUZES FOR MORTAR SHELLS 


419 


NBS T-171 Fuze 

In order to obtain a unit which would have 
the electric and mechanical systems isolated as 
much as possible, most NBS T-171 units were 
made without an out-of-line element in the 


Table 49. Times to mechanical arming of GU 
T-132. 


Charge 

Arming 

indi- 

cation 

No. of Arming time (sec) 

units Max Min Mean SD 


A rming 

setting: 2,600 turbine 

turns 


1 

FOMA 

16 4.2 

3.3 

3.7 

0.37 


CIMA 

25 4.3 

3.5 

3.8 

0.36 

2 

FOMA 

6 2.7 

2.4 

2.6 

0.10 


CIMA 

6 2.7 

1.9 

2.1 

0.30 

3 

FOMA 

6 2.3 

2.0 

2.1 

0.10 


CIMA 

6 2.7 

1.9 

2.1 

0.30 

4 

FOMA 

13 2.2 

1.7 

1.9 

0.23 


CIMA 

42 2.2 

1.6 

1.9 

0.20 


Arming setting: 2,1+00 turbine 

turns 


1 

FOMA 

24 4.2 

3.4 

3.8 


4 

FOMA 

23 3.8 

1.6 

2.0 


Table 50. Slant distance to arming of GU T-132. 


No. of Slant distance to arming (ft) 

Charge 

units Max 

Min 

Mean 


Arming setting: 2,1+00 turbine 

turns 


1 

24 

1,290 

1,070 

1,170 

4 

23 

1,200 


990 

1,110 

powder train. 

This did away with the 

gear 


train running through the entire length of the 
unit. Arming was accomplished by an RC delay 
in the firing circuit which prevented firing 
until a certain time after the generator started 
to provide plate voltage. This was strictly an 
experimental design, not intended for Service 
use. The only available datum on arming of this 
unit is the time to the earliest function ob- 
served in any test. 

Nominal Minimum 
time time 

No. of R C to arming to function 

units (megohm) (/-if) (sec) (sec) 

231 5.0 0.6 2.3 3.9 


95,4 Ranges 

Since the weight of a VT mortar fuze is rela- 
tively large compared with the weight of the 


shell, slight changes in fuze shape and size may 
result in noticeable effects on mortar shell bal- 
listics. In Table 51, the effect of fuze shape on 
range is indicated. It should be noted that the 
effect for the M-56 shell with 2-in. tail exten- 
sion is not as marked as in the case of the 
M-43C ; this is due to the fact that the drag of 
the M-56 extension shell is quite large, and the 
weight of the shell is greater. 

The weights of the fuzes, with the exception 
of the PD fuze, were approximately the same. 
The T-132A is a streamlined T-132. The T-132B 
is slightly more streamlined than the T-132A 
(see Chapter 4). Range data given for the 
T-171 are based on field tests of fuzes manu- 
factured at NBS. These fuzes had flat noses 
similar to the T-132. The T-171 fuzes manufac- 
tured by Wurlitzer had rounded caps similar to 
the T-132A, and their ranges were greater than 
those of NBS T-171. However, no data are 
available for these fuzes at an elevation of 45 
degrees. The T-172 has a loop antenna and can- 
not be compared in shape to the other fuzes. 

The effect of various mortar shell types, 
fuzed with T-132, on ranges is shown in Table 
52. Since the M-43C is lighter and smaller than 
the M-56, its range is longer. The M-56 with 
the 2-in. tail extension had the shortest range. 
(The long tail structure, with its increased 
space about the powder, caused slower burning. 
In addition, the increase in projectile length 
decreased the distance through which the pres- 
sure from powder-burning could act. The tail 
extension, however, increased the stability of 
the shell.) 

It should be remembered that the incre- 
ments of charge used with the M-43 shell are 
smaller and of a different type from those used 
with the other shells. Charge 6 for M-43 is 
roughly the same as charge 4 for M-56. 

No adjustments were made to allow for the 
effect of wind direction and velocity upon 
range. Data in Tables 51 and 52 are from field 
tests conducted at Blossom Point Proving 
Ground only. 

In Tables 51 and 52, the weights listed are 
those for fuzed projectiles. These weights are 
only approximate. In the field tests from which 
the range data were obtained, the proper func- 
tioning of the fuze was of primary interest. 


420 


ANALYSIS OF PERFORMANCE 


The shells were cavitated for permanganate 
puffs, and no special effort was made to equal- 
ize the weights. 

The figures in parentheses, following range 
values, are the number of rounds upon which 
the ranges are based. 


Since in many instances the fuzes were ini- 
tiated to combat so late in World War II, only 
preliminary or trial usages were made. Follow- 
up orders for fuzes after first trials were not 
fulfilled in time to be of value. 

The information presented in this section 


Table 51. Ranges of mortar shells: effect of fuze. 14 - 30 - 39 





Shell: M ~Ij.SC Charge: 4 



T-132 

T-132 A 

T-132B 

T-171 T-172 

PD M-52B1 

Elevation 

(7 lb, 10 oz) 

(7 lb, 10 oz) 

(7 lb, 10 oz) 

(7 lb, 10 oz) (7 lb, 12 oz) 

(6 lb, 13 oz) 

45° 

6485' (356) 

7295' (6) 7300' (6) 

Shell: M-56 + 2-in. ext. 

6445' (106) * 

9495'f (12) 

Charge: 1 



T-132 

T-132A 

T-132B 

T-171 

Elevation 


(11 lb, 10 oz) 

(11 lb, 10 oz) 

(11 lb, 10 oz) 

(11 lb, 10 oz) 

45° 


2075' (5) 

2170' (6) 

2040' (6) 

2025' (47) 

* Tests 

conducted at the Clinton Proving Ground indicate that ranges for 

T-172 on M-43C shells, fired with charge 4 at 45° quadrant 

elevation, are approximately equal to ranges for T-132 fired under the same conditions. 


t Fired 

at 46° elevation. 






Table 52. 

Ranges of mortar shells: effect of shell type (fuzed T-132). 30 Elevation: 45° 




M-43 

M-43C 

M-56 

M-56 ext. 

Charge 


(7 lb, 12 oz) 

(7 lb, 10 oz) 

(11 lb, 8 oz) 

(11 lb, 10 oz) 

1 


2610' (3) 

2980' (39) 
4315' (50) 

2500' (3) 

2075' (5) 

2 


3780' (3) 

3910' (5) 


3 


4270' (2) 

5205' (2) 

5320' (40) 

5095' (7) 


4 


6485' (356) 




96 OPERATIONAL USES OF BOMB AND 
ROCKET VT FUZES 

961 General 

The VT fuzes for bombs and rockets j were 
employed in combat against both the Germans 
and the Japanese by both the Army and Navy 
with varying degrees of success. The VT bomb 
fuzes were used in general-purpose, fragmenta- 
tion, and incendiary bombs, against antiair- 
craft (flak) positions, air fields, trains, and 
light fortifications to give maximum blast and 
fragmentation effect, and to disperse incen- 
diary material over buildings and troop con- 
centration areas. The VT rocket fuzes were 
employed in ground-to-ground, air-to-ground, 
and air-to-air roles to destroy aircraft hangars, 
aircraft on the ground, aircraft in flight, and 
to disperse fragments over light machine gun 
and mortar positions. 

j This section was prepared by Walter G. Finch, 
former captain in the VT detachment of the Army 
Ordnance Department. 


was taken from operational reports of the 
Army and Navy. 

962 Use by Army 

The U.S. Army used these fuzes operationally 
in the various theaters of operations as follows. 

European Theater of Operations [ETO] 

VT Fuzes, T-5. Approximately 50 T-5 fuzes 
were employed by the First Tactical Air Force, 
Seventh Army, during March and April 1945, 
against hangars, air fields, light and heavy gun 
positions. No reliable assessment data are 
available because the targets were in enemy- 
held territory, but informal information indi- 
cated that the results obtained were good. The 
general conclusion was that a larger number of 
these fuzes would have been used if they had 
become available about two months earlier. 

VT Fuzes, T-6. None of these fuzes was used 
in combat in ETO. However, rocket units of the 
First Army were experimenting with the use of 
these fuzes during the first months of 1945 and 


OPERATIONAL USES OF BOMB AND ROCKET VT FUZES 


421 


had fired a total of 40 units in a demonstration 
with 35 per cent random burst. 

Although there was a large percentage of 
random bursts, the general feeling for the fuze 
was high. Following the demonstration, the 
Twelfth Army Group decided that approxi- 
mately one-half of all rocket projectiles used 
by the ground forces should be fuzed for air 
burst and they immediately placed an order for 
all available T-6 fuzes. It was intended that 
these fuzes be used to assist in forcing a cross- 
ing of the Rhine. However, the crossing was 
made ahead of schedule without much difficulty. 
After this occurred, the attitude of the First 
Army toward the use of rockets had cooled to 
some extent, and the rocket units were dis- 
banded. There were approximately 79,000 T-6 
fuzes available in ETO when World War II 
ended. In the type of warfare experienced in 
ETO in the last phases of World War II 
(a fast-moving offensive), ground-to-ground 
rocket firing is not usually employed. This type 
of firing is used when the front lines are stable, 
and definite positions or areas are to be cap- 
tured and there is a shortage of artillery weap- 
ons. This was not the case in either ETO or 
the Mediterranean Theater of Operations 
[MTO]. 

VT Fuzes , T -50-El. Approximately 1,300 
T-50-E1 fuzes were employed by the Ninth 
Bombardment Group, Ninth Air Force, during 
March and April 1945. 

The initial mission was carried out on March 
15, 1945 by units of the Ninth Bomber Com- 
mand. Thirty-seven B-26 aircraft participated 
in the attack, carrying a total of 524 260-lb 
(M-81) fragmentation bombs. The target areas 
were located at Pirmasens and Neunkirchen, 
Germany, and consisted of important flak posi- 
tions guarding avenues of approach into inner 
Germany. The aircraft, flying in formations of 
three and six at 15,000 ft, released the bombs 
at 100-ft train spacing. Visual, verbal, and 
written reports indicate that the flak was re- 
duced considerably and in some cases stopped 
completely. 

Additional missions were against similar po- 
sitions with similar results. 

It was apparent that the using arms would 
have used more of these fuzes in ETO if they 


had been available there. Two days before the 
war in ETO ended, a cable was dispatched to 
the Air Ordnance Office in Washington, D. C., 
requesting immediate air shipment of 5,000 
T-50-E1 fuzes to the theater. 

Mediterranean Theater of 
Operations [MTO] 

VT Fuzes, T-5. These fuzes were not em- 
ployed operationally in MTO because of Air 
Force tactics. When the air forces employed 
rockets for use against the enemy, they sent 
their planes into combat in close proximity to 
the ground. This prohibited the use of the T-5 
fuzes because of range dispersion at shallow 
dive angles. 

VT Fuzes , T-6. The initial use of VT fuzes 
(T-6) occurred during the week of March 12, 
1945 when rocket units of the Fifth Army fired 
the 4.5-in. rockets from ground mounts for the 
first time in MTO. The target was a small ham- 
let at the foot of a mountain across a deep 
valley. It is estimated that 70 per cent of the 
100 units fired operated normally. Rockets were 
not used extensively in MTO because of the fact 
that they were too erratic, and the using and 
artillery arms did not have much confidence in 
them because of the large range dispersion. 
During March and April approximately 500 
units were used in combat; at least 70 per cent 
functioned satisfactorily. Deep interest was 
displayed in the VT fuzes for rockets by the 
using arms, and it was felt that these fuzes had 
great possibilities. 

VT Fuzes, T-50-E1. The Fifteenth Air Force 
used approximately 1,500 T-50-E1 fuzes in 
combat up to May 1, 1945. These fuzes were 
employed in 260-lb fragmentation bombs 
against enemy flak positions that defended an 
avenue of approach into Austria and Germany. 
The initial use was on April 1, 1945 when 18 
aircraft of the Fifteenth Air Force dropped 
213 260-lb fragmentation bombs (M-81) 

against four 4-gun German flak batteries lo- 
cated in six different target positions near 
Grisolera, Italy. 

The excellent pin-point bombing secured 
many near misses on three of the four batteries 
assigned. The B-24’s pilots were briefed to 
attack in two waves of nine aircraft composed 


422 


ANALYSIS OF PERFORMANCE 


of three 3-ship elements. Each element was 
assigned a separate 4-gun battery. All of the 
batteries attacked in the first wave ceased firing 
when the bombs exploded, even though one of 
the four batteries was missed by several hun- 
dred yards. Fifteen minutes after the first wave 
attacked, the second wave dropped their bomb 
load over the same positions and reported that 
all flak firing ceased as the bombs exploded. 
Both waves received light, inaccurate antiair- 
craft fire on their bomb runs which were made 
between 24,000 and 26,000 ft. No American 
planes were damaged nor were apy losses sus- 
tained. Ground scores indicated that 22 soldiers 
were killed, 18 were wounded, and one 20-mm 
gun was destroyed. 

Analysis of strike photographs taken on the 
mission indicated further that (1) there were 
a number of early bursts, (2) that when the 
fuzes functioned properly the detonation oc- 
curred approximately 17 ft off the ground, (3) 
that the distribution of fragments from each 
bomb over the ground was approximately 
circular, and (4) that the fragments were not 
uniformly dense throughout the pattern. 

Later attacks under similar conditions 
yielded results comparable to these of the first 
mission. 

VT Fuzes, T-51. The Twelfth Air Force used 
approximately 100 VT fuzes, T-51 in 260-lb 
fragmentation bombs, 500- and 1,000-lb GP 
bombs, and the 165-gal fuel tank incendiary 
bombs against enemy positions. The results of 
the combat tests indicated that the fuzes could 
be used to initiate 500- or 1,000-lb GP bombs 
or the 260-lb fragmentation bomb could be em- 
ployed successfully against personnel or equip- 
ment targets that are sheltered from ground 
level artillery projectiles or bomb bursts by 
walls, revetments, or fox holes. The users con- 
cluded that the fuzes could also be employed 
effectively in carpet bombing in support of a 
ground forces’ offensive. 

VT Fuzes, T-51 -El. The Twelfth and Fif- 
teenth Air Forces were ready to start employ- 
ing the T-51-E1 fuze when it was announced 
that the war had ended in MTO. There were 
10,000 of these fuzes on order from the Zone of 
Interior and they were scheduled for delivery 
in May 1945. 


Pacific Theater of Operations [POA] 

VT Fuzes, T-5 and T-6. None of these fuzes 
was used operationally in the Pacific War Zone. 

VT Fuzes, T-50-E1 and T-50-EU . (1) The 
total fuzes expended by the Army in POA until 
August 1, 1945, were 1,426 T-50-E1 and 1,656 
T-50-E4 fuzes. 

2. A demonstration was held on January 22, 
1945, at Saipan for introducing the VT fuzes 
into the POA. Twelve proximity-fuzed bombs 
were dropped and all the fuzes functioned prop- 
erly and gave normal heights of burst. 

3. The first VT fuze missions in POA were 

a. February 10, 1945. Target attacked: 
Air installations Iwo Jima. Ten B-24’s carried 
95 500-lb GP bombs fuzed with T-50-E4 fuzes. 
Results : Crews reported 65 per cent hit in the 
target area. Photos showed air bursts to have 
hit over a widespread area but very thinly dis- 
persed except for one heavy concentration of 
hits in the easternmost corner of the target 
area. Several bombardiers reported that a good 
percentage of the bombs exploded prematurely 
(1,500 to 2,000 ft below the formation). 

b. February 10, 1945. Target attacked: 
AA defenses, radio and radar northeast of air 
field No. 3, Iwo Jima. Results: 75 per cent of 
the 50 500-lb bombs, fuzed with T-50-E4 fuzes, 
hit in the target area. The fact that AA fire 
ceased shortly after bombs away indicate the 
possibility that this strike rendered at least 
some of the AA guns inoperative. 

4. Two additional missions were carried out 
against Iwo Jima, several against Marcus 
Island, and some at Ryukyus and Kyushu. All 
attacks were either against AA installations or 
airfields. Sketchy reports concerning stopping 
of AA fire or early functioning of some of the 
fuzes was essentially all the information re- 
ceived concerning the effectiveness of the prox- 
imity-fuzed bombs. Typical action photographs 
are shown in Figures 32 and 33. 

China, Burma, India Theaters of 
Operations [CBI] 

It is estimated that approximately 600 VT 
fuzes were expended in CBI against flak posi- 
tions and light fortifications. 

VT Fuzes, T-5 0-El and T-50-EU . (1) The 


OPERATIONAL USES OF BOMB AND ROCKET VT FUZES 


423 


Tenth Air Force expended 75 T-50-E1 fuzes 
in 260-lb fragmentation bombs against AA 
positions in the air preparation for landings at 
Rangoon. All the fuzes operated normally. 

2. The Twentieth Air Force employed 74 
T-50-E1 and 349 T-50-E4 fuzes in 260-lb frag- 
mentation and 500-lb GP bombs on two night 
raids against flak positions and light installa- 
tions. The function of the fuzes was reported 
as excellent, with AA fire stopped and huge 
fires started. This air force placed an order for 
179,000 T-51 type fuzes. 



Figure 32. Strike photograph from bomber, 
illustrating fragmentation patterns obtained on 
beach fortification area, Iwo Jima, February 17, 
1945. Patterns are from several trains of 260-lb 
fragmentation bombs, fuzed T-50-E1, released 
from 5,000 ft. (Army Air Forces photograph.) 

3. The Three Hundred and First Fighter 
Wing employed 74 T-50-E4 fuzes on August 15, 
1945 against enemy positions. Because of a 
slight overcast, it was difficult to observe the 
results. 

VT Fuzes , T-51 -El. The Fourteenth Air 
Force dropped a total of 96 T-51-E1 fuzes 
against enemy AA positions, buildings of 
Chinese construction, and entrenched personnel, 
48 on 500-lb GP bombs, 32 on 250-lb GP bombs, 
and 16 on 260-lb fragmentation bombs. In all 


cases where VT-fuzed bombs were used, they 
functioned properly and effectively. No mal- 
functions were observed. 


963 Use by Navy 

The U. S. Navy employed the VT fuzes for 
bombs with success against the Japanese. 
These fuzes were used in missions against anti- 
aircraft gun positions, light buildings, and per- 
sonnel in the open. The aircraft carrier USS 
Randolph, for example, employed a consider- 
able number of the fuzes in the last six weeks 
of World War II. From July 1 through August 
15, 1945, the carrier’s aircraft dropped a total 
of 2,240 bombs of all sizes over Japanese tar- 
gets. Of this number, approximately 800 of the 
bombs were fuzed with VT fuzes or 35 per cent 
of the total number of bombs dropped during 
the period were VT fuzed. 

Other examples of the percentage of VT 
fuzes, T-50-E1 and T-50-E4, used in combat 
during the latter stages of the war with the 
Japanese are listed below. 

From July 10 to August 15, 1945 



VT 

T-50 

Conven- 



fuze, 

type 

tional fuze, 



260-lb 

500-lb 

all types 


Aircraft carrier 

frag. 

GP 

of bombs 

% VT 

USS Bennington 

348 

170 

1,204 

30 

USS Independence 

242 

11 

431 

37 

USS San Jacinto 

212 

95 

712 

30 

USS Shangri-La 

584 

185 

1,300 

37 


Reports on Effectiveness. Following are ex- 
tracts from various Navy reports on the use of 
VT bomb fuzes. 

1. Excerpt from Report USS Yorktown for 
the period from May 24 to June 13, 1945, sup- 
port of Okinawa operations: 

VT fuzes were used with both 260-lb fragmentation 
and 500-lb GP bombs, this ship’s first experience with 
these fuzes. Pilot observations as to fuze functioning 
and bomb effectiveness were necessarily limited because 
of the high release altitudes required with these fuzes 
and the type damage done by fragmentation bombs, but 
the pilots were generally enthusiastic about the possi- 
bilities of this type of attack. The latest VT fuzes, 
which have reasonably low minimum release altitudes, 
in fragmentation bombs promise to be excellent weapons 
for use against revetted aircraft and personnel targets. 




424 


ANALYSIS OF PERFORMANCE 


2. Excerpt from brief of Commander Task 
Group 38.4, dated May 24 to June 13, 1945: 

VT fuzes were employed for the first time during this 
operation. Functioning of the fuzes appeared satis- 
factory, but an accurate count could not be obtained. 
The best available information indicates about ten per 
cent were duds, exploding on impact and another ten 
per cent exploded prematurely. Some of the prematures 
were possibly caused by close proximity to other bombs. 
The high release altitude required to arm these fuzes is 
a distinct disadvantage. Fuzes requiring shorter travel 


saturation of defenses were achieved by having all 
available VF and VBF strike a single airfield system 
in a coordinated plan over the shortest possible time 
interval. Ample time was allowed for careful target 
assignment and briefing. An approach track which 
allowed the enemy minimum warning was selected. 
Finally, a weapon was selected (260-lb fragmentation 
bombs, VT-fuzed) which apparently effectively attacked 
revetted aircraft and anti-aircraft positions. This opera- 
tion was entirely successful; considerable damage is 
estimated to have been done the enemy with the loss to 
ourselves of no pilots and only four airplanes. 



Figure 33. Strike photograph from bomber, illustrating fragmentation patterns obtained on air field 
at Tsuiki, northern Kyushu, August 8, 1945. Bombs were 260-lb fragmentation, fuzed T-50-E1, released 
from 10,000 ft. Some bombs burst over water, giving sharply defined fragmentation patterns (Army Air 
Forces photograph) . 


to arm should be made available as soon as possible. 
VT fuzes are a valuable addition to our offensive arma- 
ment, but it is felt that strafing is still the primary 
means of destroying revetted aircraft. 

3. Extract from a Task Force 38 report, 
dated June 8, 1945 : 

This operation is given separate treatment because it 
was specifically planned to avoid the difficulties of the 
previous Kyushu sweeps. Tactical concentration and 


4. Aircraft launched from the USS Ticon- 
deroga on June 9 and 10, 1945, were used to 
drop 260-lb fragmentation bombs fuzed with 
T-50-E1 fuzes and 500-lb GP bombs fuzed with 
T-50-E4 fuzes on antiaircraft positions on 
Minami Shima and Kita Shima. The pilots of 
the aircraft estimated that 90 per cent of the 
106 VT-fuzed bombs dropped functioned nor- 
mally and that the antiaircraft fire from the 




OPERATIONAL USES OF BOMB AND ROCKET VT FUZES 


425 


islands, in general, ceased after the attack. 

5. Excerpt from brief of action reports and 
analysis of strike on Wake Island, June 20, 
1945, ComCarDiv 11, USS Hancock , USS Lex- 
ington, and USS Cowmens: 

Fighters were used exclusively on anti-aircraft and 
several installations appear to have been knocked out. 
Favorable reports were made on the effectiveness of the 
air burst (VT) fuze by Air Group SIX. This group 
employed their VT bombs in what appears to be a most 
effective manner. The first dive was made for the sole 
purpose of releasing the air burst fuzed bombs, the 
second pass, using their rockets and machine guns, led 
the bombers in to the target. It is interesting to note 
that none of the Hancock bombers were hit. While the 
white phosphorus bombs seem to have functioned 
normally, it is believed that a certain amount of train- 
ing is required by the pilots carrying this bomb to 
provide practice in placing the bomb properly with 
relation to the target, and by bombers who must learn 
how to wait until the smoke cloud has had time to 
develop fully before coming within AA range. 

The attacks at Wake were characterized by more 
extensive anti-flak measures than naval A/C have per- 
haps ever used from the point of view of ordnance and 
tactics. When the strike group sighted the island at 
about 30 miles, anti-flak VF broke away, flew in ahead 
and attacked threatening AA positions with VT fuzed 
bombs (usually 260-lb frags) and White Phosphorus 
Bombs. VF then rejoined the group orbiting 10 to 15 
miles away and a coordinated attack followed with VF 
rocketing and strafing AA positions a few seconds 
ahead of VB, VT, and VBF. 

260-lb Frag M-81 with VT Fuzing: Reports of 
observers indicate that this bomb and fuzing may be 
very effective. Several AA installations, medium and 
heavy, were definitely silenced, but whether this can be 
attributed to personnel or material casualties cannot 
be determined at this time. Photographs do not reveal 
definite material damage, although it may be exten- 
sive. 

1,000-lb GP Bombs with VT Fuzes: An experienced 
ACI officer observer believes that use of this bomb must 
have caused extensive damage, although again it is not 
revealed by photographs. Bursts were just above ground 
and high enough to clear revetments. 

VT Fuzes T -5 0-El and T-50-EU: This fuze is very 
effective and must be carefully considered in planning 
bomb loading. One dud was reported although all VT- 
fuzed bombs also had tail fuzes. No prematures were 
reported. The relatively high point of release for arming 
is a disadvantage in pinpoint bombing, but the T-90 
series VT fuzes should tend to overcome this defect. The 
results of this operation indicate that VT-fuzed bombs 
should be highly effective against heavily revetted posi- 
tions, anti-aircraft positions, personnel, parked aircraft, 
and vehicles. If pilots were experienced in train release 
of VT-fuzed bombs, more practical loadings could be 


made. In this operation only one VT-fuzed bomb per 
plane was used. 

It is believed that the use of the VT-fuzed bombs by 
the anti-flak fighter planes of the Air Group was highly 
successful against anti-aircraft positions attacked on 
Wilkes Island and Wake Island. Two medium A A near 
the Marine Camp of Southwest Wake Island were 
permanently silenced after a VT bomb attack and some 
of the many guns at and near Peacock Point may have 
been knocked out. VB and VTB encountered almost no 
AA fire on their attacks although attacking VF were 
subject to fire from heavy, medium, and light AA. It is 
reasonable to believe that the VB, VRB, immunity was 
due to the anti-flak attacks preceding the bombing runs. 
Commander of VBF 6 reported that the VT-fuzed bomb 
burst left wide circular residual smoke on the ground 
estimated at least 300 ft in radius. Plainly the aerial 
bursts with their wide-spread fragmentation and blast 
damage may have inflicted substantial casualties to 
personnel, aside from their psychological and morale 
effects. 

Some uneasiness was experienced by pilots in using 
the VT-fuzed bombs at the possibility of the arming 
wire slipping out and the bomb being armed by its air 
travel while still hung on the wing rack. 

The T-50-E1 and T-50-E4 fuzes require too high 
minimum-release altitudes for accurate bombing. Issue 
of the newer T-91 and T-92 fuzes, when available, will 
materially increase the effectiveness of the VT bombs. 

This Air Group dropped a total of 42 bombs with 
VT aerial burst bomb fuzes. Very little tangible results 
could be observed from the use of these bombs. In some 
instances pilots observed slight aerial disturbances 
over targets where bombs were dropped with slight 
dust clouds and other debris. Since no personnel were 
observed, the effect of these bomb bursts against per- 
sonnel could not be ascertained. 

As target coordinator on certain strikes, I observed 
no tangible evidence of the effect of the bombs bursting 
in the air except the slight dust disturbances. No 
diminishing of AA fire can be definitely attributed to 
these bombs. Some of these VT-fuzed bombs were seen 
to explode by contact. However, due to pilots inability 
to observe bomb explosions during dives, there may 
have been many more bombs exploded by contact. 

AirPacComment : The “slight dust disturbances” 
mentioned arise from impact of fragments on the 
ground about the burst. The presence of such a dust 
pattern, and of an orange explosion and black smoke 
billowing in all directions, is evidence of an aerial burst. 
Damage visible from the air will seldom be inflicted by 
VT-fuzed bombs, but the extent of the dust pattern will 
show the extent of the pattern of lethal and damaging 
fragments. The concussion of a nearby aerial burst, par- 
ticularly of a large GP, is also likely to be somewhat 
unsettling to AA gunners. 

6. Excerpt from CO USS Coivpen’s report, 
dated June 23, 1945 : 



426 


ANALYSIS OF PERFORMANCE 


The effectiveness of subject bombs (VT fuzed) was 
difficult to observe from the air. Pilots were at times 
unable to judge whether the bombs burst on or above 
the ground, but the consensus of opinion is that the 
majority of bursts were above ground level. 

Two observed cases of reduction of AA fire after 
attack with subject bombs were noted as follows: 

(a) Medium AA fire from the vicinity of . . . ap- 
parently ceased after strikes one and two. 

(b) Heavy A A positions at . . . were attacked, and 
at least two very close air bursts were obtained. Heavy 
AA guns were observed firing from this position imme- 
diately prior to attack. Five VF aircraft of VF-50 
made a second dive on this position five minutes later, 
and all pilots stated definitely that the guns were not 
firing on the second attack. 

In the opinion of the Commander, . . . , the 260-lb 
fragmentation bomb with VT fuze is an excellent 
weapon for attacks on revetted positions and is far 
superior to WP bombs and to rockets. It is recommended 
that two such bombs per VF aircraft would make an 
excellent load for all attacks on AA positions, personnel, 
grounded aircraft or vehicles. When the 260-lb fragmen- 
tation bomb becomes available, it should be even better 
for this purpose. 

Due to the fact that salvo drops of VT-fuzed bombs 
are inadvisable, it is further recommended that, if 
practicable, VF bomb releases be rewired through the 
rocket selector box so that drops in train may be made 
more easily. 

7. Excerpt from action report USS Essex , 
July 2 to August 15, 1945: 

VT Prematures: No accurate statement can be made 
of the number of VT prematures dropped by bombers, 
but it is estimated to be below 10 per cent. The majority 
of prematures appear to have been dropped by fighters 
who released higher than bombers. It is estimated that 
the number of prematures from fighters was sometimes 
over 50 per cent. The only prominent variables involved 
were that fighters carry these bombs externally and 
that they be released at speeds 70 to 100 knots higher 
than the bombers. It is suggested that experiments be 
coffaucted to determine whether speed at release has 
any effect on premature bursts. It was the opinion of 
most of the pilots that the premature bursts were 500-lb 
GP bombs rather than 260-lb frags. There can be no 
certainty about this observation, since judgment could 
be made only from the appearance of the burst, but it is 
an indication that the fuze used with the 500-lb GP is 
more susceptible to premature functioning than the one 
used with the 260-lb frag. 

VT-Fuzed Bombs: Greatly increased damage per ton 
of bombs dropped on revetted and parked airplanes is 
believed to result from the use of T-50-E1 VT-fuzed 
frag bombs. However, somewhat less enthusiasm is felt 
for the T-50-E4 VT-fuzed 500-lb GP bombs. In the 
case of the latter, a considerably higher percentage of 
“prematures” is indicated from the overall evidence 


that is available. Further, the actual total damage per 
load of bombs is believed to be greater (assuming 100 
per cent correct fuze performance) in the case of the 
260-lb frag bombs. Also, the rather strenuous ordeal of 
the TBM to attain a climbing or cruising speed high 
enough to satisfy the SB2C’s, F6F’s, and F4U’s at 
16,000 to 20,000 ft altitude when loaded with 4 x 500-lb 
bombs, brings to issue a point in favor of the lighter 
load of 6 x 260-lb bombs. 

8. Excerpts from CNO, memo, dated July 
14, 1945: 

VT-Fuzed Bombs: On the Kanoya strike 8 June, VT 
fuzes were used for the first time. These were attached 
to all bombs released over the target area (52 260-lb 
Frag and 11 500-lb GP). Pilots observed a few pre- 
mature bursts, but the general opinion was that func- 
tioning of these fuzes was satisfactory and that the 
area was well covered with bursts exploding close to 
and above ground. 

9. Excerpt from Commander Air Force, 
Pacific Fleet on Japan Operations July 10 to 18, 
1945 : 

VT-fuzed bombs used extensively against parked A/C 
in the Tokyo district are believed to be an ideal loading 
for this type of target. Some high bursts were observed, 
but the number of these was less than the anticipated 
10 per cent. The required high release altitudes in 
reducing bombing accuracy emphasized the importance 
of issuance of the new T-91 and T-92 fuzes. 

The VT fuzes referred to were of the T-50 type. 

10. Excerpt from USS Lexington action re- 
port, dated August 4, 1945 : 

This Air Group dropped a total of forty-two (42) 
bombs with VT aerial burst bomb fuzes. Very little 
tangible results could be observed from the use of these 
bombs. In some instances pilots observed slight aerial 
disturbances over targets where these bombs were 
dropped with slight dust clouds and other debris. Since 
no personnel were observed, the effect of these bomb 
bursts against personnel could not be ascertained. 

The target coordination observed no tangible evidence 
of the effect of the bombs bursting in the air except the 
slight dust disturbances. No diminishing of AA fire can 
be definitely attributed to these bombs. A total of three 
VT-fuzed bombs were seen to explode by contact. How- 
ever, due to pilots inability to observe bomb explosions 
during dives, there may have been more bombs exploded 
by contact. 

11. Excerpt from action report, USS Ben- 
nington, dated August 31, 1945; operations 
against the Japanese homeland from Western 
Honshu to Eastern Hokkaido: 

VT Fuzes. Although positive damage assessment is 
extremely difficult, it is believed that VT fuzes have 


OPERATIONAL USES OF BOMB AND ROCKET VT FUZES 


427 


performed extremely well and that they have solved the 
long-present air burst fuze problem. If all safety pre- 
cautions are strictly followed, they are as safe as the 
conventional fuzes and no trouble whatsoever will be 
encountered. 

9 ' 6 ' 4 Summary of Conclusions Made by 
Using Arms 

An analysis of operational reports by the 
services yielded the following general conclu- 
sions : 

1. The general attitude of the using arms to 
the bomb and rocket VT fuzes at the end of 
World War II was most favorable. Originally 
there was much doubt as to their possible value 
as a lethal weapon. The general attitude was 
that the fuzes had very limited use, that they 
were unsafe, and that a high percentage of 
them malfunctioned. Combat experience in the 
various theaters changed this view, and with 
the close of World War II the using arms were 
very enthusiastic over the fuzes. 

2. The operational use of VT bomb and 
rocket fuzes, particularly in ETO and MTO, 
was retarded by transmission to the theaters 
(by the AAF) of unfavorable data taken at 
Eglin Field on preproduction fuzes. This infor- 
mation caused a feeling that the fuzes were 
not ready for operational use at that time and 
necessitated a great deal of experimenting in 
the combat area to see if they performed satis- 
factorily and were safe. Exhaustive preopera- 
tional tests were conducted in both ETO and 
MTO before employing the fuzes operation- 
ally. 

3. These fuzes could be used effectively to 
explode 260-lb fragmentation bombs or 500- or 
1,000-lb GP bombs on personnel or equipment 
targets that were sheltered from ground level 
artillery projectiles or bomb bursts by walls, 
revetments, or fox holes. 

4. These fuzes could be used effectively in 
carpet bombing in close support of a ground 
force offensive. It was felt that an area could 
be saturated with bomb fragments at an angle 
that is most effective against personnel occupy- 
ing defensive positions. 

5. These fuzes could be used effectively for 
neutralizing concentrated flak positions, such 


as were found on many of the Pacific islands. 
Bombers at high altitudes can identify flak 
positions and drop 260-lb fragmentation bombs 
with VT fuzes accurately enough to cause a 
diminution of accuracy and intensity of AA op- 
position. 

6. These fuzes could be used effectively with 
500- and 1,000-lb GP bombs mounted under the 
wings of fighter aircraft. 

7. The T-5 and T-6 type fuzes had very lim- 
ited use because of our superiority in airpower 
and the high dispersion of the M-8 rocket. 

8. The T-50-E1 and T-50-E4 type fuzes gave 
an operational performance of 70 to 75 per cent 
in actual combat, based on reports submitted 
from the various theaters. These figures are 
lower than test results of 80 to 85 per cent 
obtained in the United States, and this is prob- 
ably due either to incomplete counts or to poor 
installation of the fuzes in the combat areas. 

9. Ground reports from special agents indi- 
cate that fragmentation bombs with VT fuzes 
reduce morale and accuracy of flak personnel, 
kill and injure flak personnel, and cause dam- 
age to AA equipment, such as cables, directors, 
and radar units. 

10. In attacking flak positions, it was found 
by the Ninth and Fifteenth Air Forces that the 
best tactics were to attack each position in ele- 
ments of threes instead of a large number of 
planes in close formation. 

11. In addition a number of suggestions 
were made for improving or modifying the 
fuzes. These included 

a. That the percentage of random bursts, 
especially the early bursts, be reduced both for 
psychological and economic reasons. 

b. That arming delays be supplied with 
all bomb fuzes being shipped in order to im- 
prove fuze performance and give an added 
margin of safety whenever possible. 

c. That provision be made for shorter 
arming times, particularly for dive bombing. 

d. That extra lock washers be supplied 
with shipments of the fuzes, since they are usu- 
ally flattened during installation or removal of 
the fuzes. 

e. That a streamlined windshield be de- 
veloped to cover the arming vane for those 
fuzes that are employed in bombs that are 



428 


ANALYSIS OF PERFORMANCE 


mounted under the wing racks in fighter type 
aircraft. 

f. That corrective measures be insti- 
tuted to eliminate breaking of cotter pins on 
arming vanes and thus causing duds. 

g. That a suitable wrench be shipped 
with the fuzes for tightening the fin-locking 
nuts on the various bombs. 

h. That improvements be made in the 
arming wire method of preventing vane rota- 
tion, with particular attention to bombs car- 
ried under the wings of fighter planes. Al- 
though the arrangement appeared satisfactory 
when properly installed, an error in installation 
would allow the arming wire to be pulled out by 
air drag while still mounted on the wing. 


9 7 SUMMARY AND CONCLUSIONS 

Pertinent summary data of this volume on 
radio proximity fuzes were presented in the 
introduction, particularly in Sections 1.4 and 
1.5. The reader may therefore refer to Chapter 
1 for summary information. 

With proximity fuzes established as impor- 
tant and practicable ordnance items, it is desir- 
able that development work continue. In the 
various preceding chapters, as well as in this 
chapter, the limitations and deficiencies of the 
fuzes developed during World War II have 
been discussed. Future work will naturally at- 
tempt to eliminate these deficiencies. It has 
been pointed out in several places in the vol- 
ume that numerous compromises in design 
were necessary for reasons of expediency. In 
an orderly long-term peacetime development, 
such compromises should be less difficult to re- 
solve. 

A detailed discussion of the limitations of the 
fuzes previously described and methods for 
improvement should not, however, be made 
here, for two important reasons. 

1. Advanced thinking and more sophisti- 
cated development on radio proximity fuzes 
will be classified “secret” much longer, accord- 
ing to present classification policy, than will the 
material presented in this volume. Accordingly, 
the possible circulation of this volume would be 
appreciably curtailed by including, just in sug- 


gestive form, some of the most promising ideas 
for fuze improvements. The material in this 
volume has been presented, as far as possible, 
in a form to provide a basis for further devel- 
opment. The subject matter of Chapter 2, in 
particular, is fundamental to any fuze design 
which involves the interaction of radio waves 
with a target. Thus, it does not seem desirable 
to impair the possible usefulness of this volume 
by including a little new and much more re- 
stricted material which is of unproven merit. 

2. One of the main reasons for outlining sug- 
gestions for possible future work is to urge that 
such work be undertaken. The Army Ordnance 
Department, one of the agencies to whom this 
report is made, has already formulated a vig- 
orous fundamental development program on 
proximity fuzes. Assumption of responsibility 
for further development was started by the 
Army prior to the end of World War II and is 
continuing. Division 4’s central laboratories, 
the Ordnance Development Division at the Na- 
tional Bureau of Standards, are now working 
for the Army Ordnance Department on new 
fuze problems. Thus, with an active far-reach- 
ing program on proximity fuzes already under 
way, it becomes superfluous to suggest here 
what form that program might take. 

The important thing is to insure that the ac- 
cumulated technical information and experience 
of World War II period is available in an orderly 
form for those who will continue the work. It 
is hoped that the preceding pages of this vol- 
ume have fulfilled that objective. 


98 APPENDIX TO CHAPTER 9 

ACCEPTANCE TEST CONDITIONS 

981 Acceptance Testing of Bomb Fuzes 

A program for acceptance testing of VT 
bomb fuzes was established early in 1944. Since 
then minor variations in acceptance require- 
ments have been made. Basically the testing 
procedure has remained unchanged. Every 
manufacturer’s lot, considered for acceptance, 
was subjected to two types of field tests : a metal 
parts assembly test, followed after acceptance 
by a loading test of ammunition lots, which 


APPENDIX TO CHAPTER 9 


429 


usually involved several metal parts lots. An 
outline of Army Ordnance specifications for 
these tests follows : 51 

A. Metal Parts Test 

1. A ballistic sample of 18 metal parts assemblies 
(fuzes) prepared for testing will be shipped to the 
Proving Ground from a loading plant. 

2. Metal Parts to be tested will be assembled to 
bombs, as follows : 

a. T-50-E1, T-89— Bomb, Frag, 260 lb, 
AN-M81. 

b. T-50-E4, T-90— Bomb, GP, 500 lb, AN-M64. 

c. T-51, T-51-E1— Bomb, Frag, 260 lb, 
AN-M81 or Bomb, GP, 250 lb, AN-M57. 

d. T-91— Bomb, Frag, 260 lb, AN-M81. 

e. T-92— Bomb, GP, 500 lb, AN-M64. 

The AN-M64 and AN-M57 will be sand loaded. The 
AN-M81 may be used empty (empty-weight 220 lb). 
The bombs should be equipped with a suitable spotting 
charge. Every precaution will be taken that both the 
fuze and tail fin assembly are tightly screwed to the 
bomb. (Not possible to unscrew by hand. A wrench is 
provided to tighten the fuze.) 

3. All bombs will be dropped singly in the normal 
manner from an aircraft flying at a true air speed of 
200 ± 5 mph from a true altitude of 10,000 — 1,000 ft 
above the target. 

4. Normal Test Plan. 

a. Seventeen metal parts assemblies will be 
tested for a first sample. 

b. Requirement for Acceptance — 12 or more 
assemblies shall cause proper functioning. 

c. Retest sample will contain 23 metal parts 
assemblies. 

d. Requirement for Acceptance on Retest — 26 
or more assemblies. 

5. Reduced Test Plan. (This plan was discon- 
tinued April 3, 1945 by order of Army Ordnance.) 

a. Six metal parts assemblies will be tested 
for the first sample. 

b. Requirement for Acceptance — 5 or more 
assemblies must cause proper functioning. 

c. Twelve metal parts assemblies will con- 
stitute a retest sample. 

d. Requirement for Acceptance on Retest — a 
total of 10 or more assemblies out of the entire 18 
tested shall cause proper functioning. 

6. The following procedure applies to the Reduced 
Testing Plan of Paragraph 5 above: 

a. If 10 successively produced lots offered for 
acceptance by a manufacturer are accepted under the 
Normal Test Plan the producer is placed on a preferred 
list which entitles him to have his product tested on the 
basis of the reduced testing criterion. 

b. Such a manufacturer will remain on this 
basis until a lot is rejected on the basis of the Reduced 
Test Plan. The producer will then return to the Normal 
Testing Plan basis. 

c. Requalifi^ation as explained in (a) above 


will be necessary in order for the manufacturers 
product to be again tested on the Reduced Testing Plan. 

7. Height of burst for proper function will de- 
pend on the nature of the target area. If the metal parts 
assemblies are tested over water the height of burst for 
proper functions are fixed and are listed below. If the as- 
semblies are tested over land the required heights for 
proper function shall be determined by multiplying the 
required height range for testing over water by a target 
factor which is to be determined at least twice during 
the testing period of a day. This factor depends upon 
variables of the target area. Necessary equipment to 
obtain this information and personnel to install and 
instruct in its use will be arranged through the Office, 
Chief of Ordnance. The following figures constitute the 
range of proper functioning when the fuzes are tested 
over water: 

T-50-E4, T-50-E1, T-89, T-90, T-91 and T-92- 
between 10 and 160 ft. 

T-51, T-51-E1 — between 60 and 240 ft. 

B. Loading Tests 

1. Accepted metal parts lots will be received at 
the loading plant and be assembled into a grand lot for 
loading. Lot for loading will generally consist of more 
than one metal parts lot of one manufacturer. From 
each loaded lot a ballistic sample of 20 fuzes will be 
shipped to the Proving Ground for test. 

2. The sample sent to the Proving Ground will be 
tested for the following qualities : 

a. Minimum Safe Air Travel (abbreviated 
MinSAT). 

b. Functioning quality of the loading com- 
ponents. 

3. The Loading tests will consist of 2 phases. 
Phase 1 is a test of the MinSAT of the lot and con- 
ducted with inert bombs ; phase 2 is a test of functioning 
quality of the lot and is conducted with HE bombs. 
Phase 1 is based upon an altitude of release from which 
no arming should occur before impact. Phase 2 is based 
upon an altitude of release from which the majority of 
the fuzes should arm before impact. 

4. Arming of VT bomb fuzes is dependent upon 
the size and shape of the bomb as well as its ballistic 
character of flight; therefore, it is desirable to conduct 
phase 1 of the test on the bomb which will give the fuze 
the least MinSAT with which that particular model of 
fuze may be used. At present this bomb is the AN-M30 
or the AN-M81 for all models. 

5. Below are tabulated the requirements for con- 
ducting Loaded Acceptance Tests of VT bomb fuzes. 

6. Phase 1 may be released in train at any desired 
interval and should impact on normal soil. Phase 2, if 
desired, may be released in train providing AN-M30 and 
AN-M81 bombs are spaced with at least 50 ft. interval 
and AN-M57 and AN-M64 are spaced with at least 100 
ft. interval. Phase 2 may be tested over water or land. 
Phase 2 should not be conducted if a lot fails on phase 1. 

7. A lot of fuzes should be rejected if it fails to 
meet the requirements of either phase 1 or 2 of this test. 


430 


ANALYSIS OF PERFORMANCE 


Upon rejection, a retest will be authorized only by the 
Office, Chief of Ordnance. 

98 2 Acceptance Tests of Navy Rocket 
Fuzes 

A procedure similar to that used for bomb 
fuzes was followed in the acceptance testing of 


the T-2004 rocket fuze. The major part of the 
rocket testing program was done in accordance 
with Army Ordnance specifications of May 
1945. 52 * 53 A summary of these specifications is 
given below. 

A lot was tested in two phases : first a metal 
parts test, and then, provided the first had been 
passed, a loading acceptance test. 



Fuze, Bomb, 

Nose, VT, T-50-E1 & T-89, 

3,600 ft MinSAT (Sample Containing 20) 



True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph)* 

tude (ft)* 

for acceptance 

1 

10 

fAN-M81 inert (empty) 

200 

1,750 — 200 

10 duds 



with spotting charge 

, , 




5 

AN-M30 HE 

200 

3,200 + 200 ( 

8 or more high- 

2 

5 

AN-M81 HE 

200 

3,200 + 200 \ 

order functions 


Fuze, Bomb, 

Nose, VT, T-50-E4 & T-90, 

3,600 ft MinSAT (Sample Containing 20) 




True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph)* 

tude (ft)* 

for acceptance 

1 

10 

fAN-M81 inert (empty) 

200 

1,750 — 200 

10 duds 



with spotting charge 





5 

AN-M30 HE 

200 

3,200 + 200 ) 

8 or more high- 

2 

5 

AN-M64 HE 

200 

4,100 + 200 S 

order functions 


Fuze, Bomb, 

Nose, VT, T-51 or T-51-E1, 

3,600 ft MinSAT (Sample Containing 20) 




True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph)* 

tude (ft)* 

for acceptance 

1 

10 

AN-M81 (empty) with 
spotting charge 

200 

1,700 — 200 

10 duds 






8 or more high- 

2 

10 

AN-M57 HE 

200 

3,400 + 200 

order functions 


Fuze, Bomb, 

Nose, VT, T-51 or T-51-E1, 

4,500 ft MinSAT (Sample Containing 20) 




True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph)* 

tude (ft)* 

for acceptance 

1 

10 

AN-M81 (empty) with 
spotting charge 

200 

2,400 — 200 

10 duds 






8 or more high- 

2 

10 

AN-M57 HE 

200 

4,500 + 200 

order functions 


Fuze, Bomb, Nose, VT, T-91, 2,000 ft MinSAT (Sample Containing 20) 





True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph) * 

tude (ft)* 

for acceptance 

1 

10 

fAN-M81 inert (empty) 
with spotting charge 

200 

600 + 100 

10 duds 


5 

AN-M30 HE loaded 

200 

3,900 + 200 

4 or more high- 



with Arming Delay, Air 
Travel T2E1 set at 3 
Divisions 



order functions 

2 

5 

AN-M81 (empty) with 

200 

1,350 + 200 

4 or more func- 



spotting charge 



tions 


Fuze, Bomb, Nose, VT, T-92, 2,600 

ft MinSAT (Sample Containing 20) 





True air- 

True alti- 

Requirements 

Phase 

Quantity 

Bomb 

speed (mph) * 

tude (ft) * 

for acceptance 

1 

10 

•|AN-M81 (empty) with 
spotting charge 

200 

900 — 200 

10 duds 

2 

5 

AN-M30 HE loaded 

200 

3,900 + 200 

4 or more high- 



with Arming Delay, Air 
Travel T2E1, Dial Set- 
ting at 3 Divisions 



order functions 


5 

AN-M64 empty (sand- 

200 

2,400 + 200 

4 or more func- 



loaded to weight) with 
spotting charge 



tions 

* The true altitude and true airspeed at release should be carefully adjusted as the results of this test depend nearly entirely upon them. 

Only level flight, true altitude and true airspeeds as listed will give the 

correct results. 



t If AN-M81 empty bombs are 

not available, AN-M30 sand-loaded 

bombs may be used. 




SECRET*. 


APPENDIX TO CHAPTER 9 


431 


Metal Parts Test. In general, 17 fuzes from 
each manufacturer’s lot tested were fired over 
water on 3.25-in. Mk-7 motors with empty 
3.5-in. Mk-5 heads. The rockets were launched 
singly from a ground rail installation with a 
firing elevation of approximately 30 degrees. 

Fuzes from every tenth lot, however, were 
fired from a plane over a water target at any 
convenient dive angle not less than 20 degrees. 
Plane speeds were approximately 250 mph. 

Requirements for acceptance: Twelve or 
more units were required to function properly 
on approach to water. (Mid-flight functions 
after 6 sec of flight time were considered proper 
functions.) Proper function height limits were 
10 to 100 ft. No function was to occur before 
450 ft of air travel. 

In case of failure a retest of 23 additional 
units was made. Twenty-six of the total of 40 
units tested were required to function as indi- 
cated above. 

Loading Test. Lots which had passed the 
metal parts test were loaded at Picatinny Ar- 
senal and combined into larger lots. These were 
subjected to a mechanical arming test and to a 
functioning test. 

Mechanical arming test: Ten fuzes, wired to 
function on mechanical arming, were fired on 
3.25-in. Mk-7 motors with 5.0-in. Mk-1 HE 
heads. The rockets were launched singly from a 
ground rail installation at any convenient eleva- 
tion. 

All fuzes were required to function between 
290 and 650 ft of air travel. The failure of more 
than one fuze to cause the rocket to burst with 
a high-order detonation caused rejection of a 
lot. 

If a lot failed, a retest of 20 additional fuzes 
could be made at the request of the contractor, 
provided (1) no burst had occurred before 290 
ft, (2) not more than one burst had occurred 
after 650 ft, and (3) not more than two fuzes 
had failed to cause the rocket to burst with a 
high-order detonation. 

For acceptance of a retested lot, it was re- 
quired that on the basis of the total of 30 fuzes 
tested (1) no burst occur before 290 ft, (2) not 
more than two bursts occur after 650 ft, and 
(3) not more than three fuzes fail to cause the 
rocket to burst with high-order detonation. 

Functioning test: Ten fuzes, set for normal 
functioning, were fired over water on 3.25-in. 
Mk-7 motors with 3.5-in. empty Mk-5 heads. 
Rockets were launched singly from a ground 


rail installation at an elevation of approxi- 
mately 30 degrees. 

A lot was accepted if no fuze functioned be- 
fore 450 ft of air travel and not more than two 
fuzes failed to function. 

If a lot failed, a retest of 20 additional fuzes 
could be made at the request of the contractor. 
The retested lot was accepted provided on the 
basis of 30 fuzes tested (1) no burst occurred 
before 450 ft, and (2) not more than four fuzes 
failed to function. 

A number of lots tested under this program 
were accepted despite the fact that they failed 
to meet the requirements of the mechanical 
arming test. It was later found that, with high 
ambient temperatures, the air travel was in- 
sufficient for the 100 propeller turns under ac- 
celeration necessary for the first stage of the 
arming process. In August 1945, revisions were 
made in the original specifications. 54 * 55 All lots 
which were retested under the new specifica- 
tions passed. The highlights of the changes 
made follow. 

Metal parts test 

1. Testing from aircraft was eliminated. 

2. Proper function limits required for accept- 
ance were made 10 to 70 ft, with an average 
height of about 35 ft. 

Mechanical arming test 

1. Projectile: 3.25-in. Mk-7 motor with 3.5- 
in. Mk-5 head. 

2. All functions were required to occur be- 
tween 300 and 850 ft of air travel. 

3. Retest requirements were changed in ac- 
cordance with these new limits. 

Loading -functioning test 

1. Projectile: 3.25-in. Mk-7 motor with 5.0- 
in. Mk-1 head (inert loaded to 48 lb). 

2. Rockets were to be fired over ground from 
a plane at any convenient dive angle less than 
20 degrees, and at an altitude to give a mini- 
mum flight time of 4 sec. Plane speed: 275 mph 
approximately. 

3. Requirements for acceptance: No fuze 
should function before 1.9 sec flight time; not 
more than two fuzes should fail to function. 

4. Corresponding changes were made in re- 
test conditions. 

9 8 3 Acceptance Testing of T-5 Fuzes 

From February 1943 to May 1944, acceptance 
tests were made on 365 lots of T-5 fuzes. For 
the first six months, the tests were conducted 


432 


ANALYSIS OF PERFORMANCE 


by NBS at Fort Fisher and Blossom Point. The 
mock-plane targets and firing towers used at 
these proving grounds are described in Chap- 
ter 8. Later testing was conducted by Army 
Ordnance at Aberdeen Proving Ground. A rec- 
tangular wire mesh screen, stretched between 
four poles, was used as the target there. 

The acceptance requirements at all three 
proving grounds were essentially the same. 
Salient features are given below. 

Test Procedure. Twenty units, from each lot 
of 1,000 to be tested, were mounted on Revere 
or Budd 4V2-in. rockets, and fired horizontally 
from a tower for function on approach to a tar- 
get approximately 70 ft above ground. 

Requirements for Acceptance. At least ten 
units were required to function properly. In a 
considerable part of the testing, firing was 
stopped as soon as ten proper functions were 
obtained. 


Method of Scoring. In order that a unit be 
counted in scoring, it had to pass within the 
radius of action of the target. For the mock- 
plane targets used at Fort Fisher and Blossom 
Point, the scoring region was defined by a circle 
of 60-ft radius, cut off by a plane 40 ft above 
the ground (because of the possibility of ground 
firing) . 

Functions were classified as proper, early, 
late, or dud. A proper function was one occur- 
ring not more than 60 ft before the center of 
the wing of the mock-plane target, and not later 
than 35 ft after. Functions occurring before 
and after the proper-function limits were clas- 
sified as earlies and lates respectively. A dud 
was a unit which failed to function. 

Retest conditions: If a lot failed the normal 
test, 60 additional units were fired. At least 44 
proper functions, based on the total of 80 units 
tested, were necessary for acceptance. 



GLOSSARY" 


/ 


A. Approach. Representing fuze function on approach 
to ground target. 

A Voltage. The voltage applied to the filaments of 
vacuum tubes. 

A Winding. The winding or coil on the generator 
power supply which furnishes A voltage. 

Afterburning. Afterburning is burning in the rocket 
motor occurring after the main burning or accelera- 
tion period. See Sections 9.2 and 9.3. 

Amplifier. That part of a radio proximity fuze which 
amplifies the doppler signal to a magnitude sufficient 
to fire a thyratron. 

Amplifier Gain. Ratio of amplifier output voltage to 
amplifier input voltage. 

Antenna. The radiator or exciting portion of a radio 
proximity fuze; the bars in a transversely excited 
fuze, the ring in a longitudinally excited fuze, the 
conical cap in the T-5 fuze, or the loop in the T-172. 

Antenna Gain. Ratio of the power transmitted per 
unit area in a given direction relative to that from 
an isotropic antenna having the same total radiated 
power. See Section 2.8. 

Antenna Reactance. The reactance occurring in the 
parallel resistance-reactance combination which is 
equivalent to the antenna. See Section 2.7. 

Antenna Resistance. The resistance occurring in the 
parallel resistance-reactance combination which is 
equivalent to the antenna. See Section 2.7. 

Approach Angle. The angle between the trajectory 
of a missile and the vertical on approach to the 
ground. 

Arming. Removal of the mechanical and electrical 
barriers to the operation of the explosive train in a 
fuze prior to which an activating signal in the fuze 
cannot cause detonation. 

Arming Angle. The angle through which the de- 
tonator rotor turns to complete the arming cycle. 

Arming Delay. The time delay between launching of 
the missile to completion of arming. The term some- 
times applied to the T-2 delayed arming device. See 
Section 4.2. 

Arming Pulse. An electrical disturbance sometimes 
arising when the detonator circuit is closed. 

Arming Wire. A wire attached to an aircraft which 
prevents initiation of the arming cycle until the bomb 
or rocket has left the aircraft. 

Audio. An adjective applied to electrical circuits or 
appropriate signals having frequencies in the audible 
range. It usually refers to the detected doppler signal. 

B Voltage. The supply voltage for the anodes of the 
electronic tubes. 

B Winding. The high voltage winding of the gen- 
erator. 

Bar Type. A transversely excited radio proximity 
fuze using a center-fed transverse bar as an antenna. 

a Many of the terms included in this glossary may not occur in 

the text but occur frequently in the references given in the 

Bibliography. 


BRLG. (Bomb, Radio, Longitudinal, Generator.) An 
early designation for a generator-powered ring-type 
bomb fuze. 

Brown. A code term for 75 megacycles per second. 

BRTB. (Bomb, Radio, Transverse, Battery.) An early 
designation for a battery-powered bomb fuze with 
transverse antenna. 

BRTG. (Bomb, Radio, Transverse, Generatpr.) An 
early designation for a generator-powered radio 
proximity fuze with transverse antenna. 

BTL. Bell Telephone Laboratories, Inc. 

Burst Surface. A hypothetical surface surrounding 
the target, showing the locus of fuze bursts upon 
approach to the target. 

C. Capacitance. 

C Bias or Voltage. The supply voltage for biasing 
the pentode and thyratron. 

C or Cv. An abbreviation for C voltage. 

Camera Obscura. The usual camera obscura tech- 
nique applied to observation of fuze function. 

Cap. The ring or conical cap used as an exciting 
antenna. 

Carrier. The radio frequency signal generated by the 
fuze oscillator. 

CCM. Counter-countermeasures. 

CF. Carrier frequency. 

CIMA. Carrier indication of mechanical arming. See 
Section 8.3. 

CM. Countermeasures. 

Compensated Load or Resistor. A dummy antenna 
resistor with inductance to simulate the actual 
antenna load. 

Corncake. The proving ground at Fort Fisher. 

Critical Grid Voltage. The maximum bias (negative) 
at which the thyratron will fire. 

D. Dud. 

Delayed Arming Device. An auxiliary wind-driven 
delay mechanism which locks the windmill for a pre- 
set distance of air travel. See Section 4.2. 

Demagnetizing. Refers to the process of reducing the 
magnetic pole strength of a generator rotor to the 
appropriate value. 

Detonator. A device which initiates an explosive 
train in response to an electrical current. 

Diode. A two-element electron tube used as the 
rectifier of the doppler signal. 

Diode Impedance. The resistance which, when in- 
serted in series with a perfect diode, would make it 
behave like an actual diode. 

Directivity Pattern. A polar plot of the antenna gain 
as a function of angle. See f 2 (0) in Section 2.8. 

Doppler Effect. The shift in frequency produced by 
relative motion between transmitter and receiver. 

Doppler Frequency. The difference or shift frequency 
produced by the doppler effect. 

Driver. A term applied to the windmill or turbine 
used as the prime mover of the generator. 

Dud. A fuze which does not function. 


433 


434 


GLOSSARY 


Dumping. The discharge of the thyratron plate con- 
denser (in a fuze having RC arming) with in- 
sufficient current to fire the detonator. See Section 
3.3.6. 

E. Early function. Function or operation of the fuze 
after arming and before reaching the target some- 
times, particularly in the case of rockets, confined 
to the first 5 seconds of flight. 

Effective Critical Voltage. The critical voltage of 
the thyratron in a fuze under operating conditions 
but in the absence of target signal. See Section 3.3.2. 

Electrical Arming. Completion of electrical circuits 
necessary to produce arming in a bomb fuze. This 
usually occurs slightly ahead of mechanical arming, 
in bomb fuzes. In fuze with RC arming, electrical 
arming occurs after mechanical arming. 

. Emerson. Emerson Radio and Phonograph Corpora- 
tion. 

Feedback Network. The network in an amplifier 
which returns a portion of the output signal to the 
amplifier input for controlling the gain frequency 
characteristic. See Section 3.2.3. 

Field Test. A functional test of a fuze on a missile 
in flight. 

Final Test or Final Test Position. Laboratory test 
or equipment for making the test on the completed 
electronic subassembly of the fuze. See Section 7.9. 

Firing Indicator. A laboratory device (usually com- 
prising a neon lamp) to indicate the firing of the 
thyratron. 

Firing Voltage. The signal input to an amplifier re- 
quired to fire the thyratron, usually measured in 
millivolts. Cf. MvF. 

FOMA. Function on mechanical arming. See Section 
8.3. 

Frequency, Audio or Doppler. See doppler frequency. 

Frequency, Carrier. See carrier frequency. 

Frequency, Generator. The frequency of the alter- 
nating current produced by the generator. 

Frequency, Microphonic. The frequency of the 
microphonic disturbances. 

Frequency, Rotational. The rotational frequency of 
the wind-driven generator system. 

Frequency Response Curve. A plot of amplifier gain 
versus audio frequency, usually plotted on log-log 
paper. 

g. Unit of acceleration; viz., 32.2 feet per second per 
second. 

Gain, Antenna. See antenna gain. 

Gain, Audio. See audio gain. 

Gain, Flat. The gain of the audio amplifier with the 
feedback network disconnected. 

Gain, Nonregenerative. See gain, flat. 

Gain-Frequency Characteristics. See frequency re- 
sponse curve. 

Gear Train. A speed-reducing train of gears inter- 
posed between the windmill and mechanical arming 
system. 

Gimmick. A small variable capacitor composed of 


twisted insulated wires, used to adjust the amplifier 
feedback. 

Green. The code term for 150 megacycles per second. 

Grid Reaction. The variation of grid bias with 
oscillator load. See Section 3.1.2. 

HD. Heard dud. A dud in which the carrier signal of 
the fuze is observed. 

Head-on Doppler. A doppler frequency for head-on 
approach to an airplane target. 

Holding Bias. The excess of the applied thyratron 
bias over the effective critical voltage. 

Hum. The high-frequency audio signal output of the 
amplifier occurring at generator frequency, and 
usually due to modulation produced by a-c operation 
of the filament. 

Hum Injection. A portion of the filament voltage 
injected into the amplifier to cancel the inherent hum. 
See Section 3.2.3. 

Impact Parameter. The perpendicular distance from 
the missile trajectory to an airplane target. 

Impeller. A term sometimes, but inaccurately, ap- 
plied to a windmill or turbine prime mover generator. 

Induction Field. That component of the transmitted 
electromagnetic field which varies inversely as the 
square of the distance from the transmitter. See 
Section 2.10. 

Jamming. A countermeasure to produce malfunction 
of fuzes by radio methods. 

L. Late. A fuze function lower than expected from 
the normal distribution of function heights or (in 
the case of an antiaircraft fuze) a function beyond 
a statistically expected burst surface. 

Load. Electrical load on an oscillator. 

Load Resistor. A resistor used as an equivalent of 
the antenna load. Cf. compensated resistor and Sec- 
tion 7.2. 

Longitudinal. Referring to a fuze system in which 
the predominant radiating current flows along the 
axis of the missile. 

M. Middle function. A random function occurring more 
than 5 seconds after launching. 

M Wave. The actual audio signal produced by the 
doppler effect of the target on the fuze. This term is 
particularly applicable to the nonsinusoidal doppler 
signal generated in approaching an airplane target. 
See Sections 2.11 and 2.12. 

Mechanical Arming. Removal of the mechanical 
barrier in the explosive train. In the case of RC arm- 
ing, it usually implies also the closing of the elec- 
trical contacts to initiate the RC arming cycle. 

Michigan Sensitivity. The theoretical height at 
which a fuze would function when approaching 
ground at optimum velocity with optimum orienta- 
tion of the missile, usually approximately horizontal. 

MRLG. (Mortar, Radio, Longitudinal, Generator.) 
An early designation for the T-132 mortar fuze. 

MROG. (Mortar, Radio, 0 for loop, Generator.) An 
early designation for the T-172 mortar fuze. 

Mutual Interference. Jamming of one fuze by an- 


GLOSSARY 


435 


other in too close proximity. Cf. sympathetic func- 
tion. 

MvF. Cf. firing voltage. Generally used as inverse 
measure of amplifier gain. 

A 7 . Number. Usually referring to number of rounds 
in a field test. 

NBS. National Bureau of Standards. 

NDRC. National Defense Research Committee. 

Normal Critical Voltage. The thyratron critical 
voltage in the absence of microphonics from the 
oscillator. 

Normalization. The process of demagnetizing a gen- 
erator rotor to give correct supply voltages. 

OD. Designation for the oscillator-diode type of fuze. 

ODD. Ordnance Development Division of the National 
Bureau of Standards. 

OSRD. Office of Scientific Research and Development. 

P. Proper function of the fuze on approach to the 
target. 

Peak Gain. The maximum gain of an amplifier. 

Philco. Philco Radio and Television Corporation. 

PkMvF. Millivolts to fire at the frequency of peak 
gain. Cf. MvF. 

Plate Reaction. The variation of the oscillator plate 
current in response to a change of high-frequency 
load on the oscillator. 

Potato Masher. A term applied to the encasing can 
for generator-powered bomb fuzes. See Figure 18, 
Chapter 4. 

POA. Puff on approach. Refers to spotting charge in- 
dication of function on approach to target. 

POD. Power-oscillating detector. A type of plate re- 
action oscillator operating at relatively high power 
level. 

POW. Puff on water. Cf. POA. 

Predicted Height. Height of function predicted on 
the basis of laboratory measurements of overall fuze 
sensitivity. 

Propeller. A term used to indicate the externally 
mounted windmill or driver for the generator. 

Pulse Test. An overall test of a fuze assembly com- 
plete except for detonator, indicating that all cir- 
cuits are functioning. 

Purge Pellet. A pellet of specially rapid burning 
material to purge the combustion chamber of residual 
propellant after the burning is essentially complete. 
See Section 9.2 on afterburning. 

Q. A figure of merit for a tuned circuit or a reactor. 

Quasi Static. The component of the electromagnetic 

field which varies inversely as the cube of the distance 
from the transmitter. See Section 2.10. 

R. Resistance. 

Radiation Field. That component of the transmitted 
electromagnetic field which varies inversely as the 
distance from the transmitter. See Section 2.8. 

Radiation Load. Radiation resistance. The com- 
ponent of the antenna resistance representing radia- 
tion losses. 

Radiation Pattern. A polar plot of radiation field 
strength versus angle, /(0). See Section 2.8. 


/ 

Random Function. A fuze function after arming and 
before the target is reached. 

RC. Resistance-capacitance network or the time con- 
stant of such a network used for time delay of elec- 
trical arming in some fuze models. See Section 3.3.6. 

Raytheon. Raytheon Manufacturing Company. 

Red. Code designation for 130 megacycles per second. 

Reflection Coefficient. Ratio of reflected to incident 
field strength. 

Regulation Circuit. A resistance-capacitance net- 
work incorporated in the power supply to maintain 
an output voltage or voltages essentially independent 
of generator speed above a limited minimum speed. 

Resistance Sensitivity. A measure of the differential 
voltage produced by an oscillator under change of 
load resistance. See Section 3.1.2. 

RGD. Reaction grid detector. Cf. grid reaction. 

Ring Type. A generator-powered fuze in which the 
antenna consists of a ring surrounding the windmill. 

Ripple Voltage. See hum voltage. 

ROA. Radius of action. The maximum radius of a 
hypothetical burst surface enclosing an airborne 
target. See also the definition in Section 5.1.3. 

ROB. Radio-operated bomb. A very early generic 
designation of radio proximity fuzes for bombs. 

ROR. Radio-operated rocket. Cf. ROB. 

Rotor, Detonator. The moving portion of the me- 
chanical barrier to an explosive train (in bomb 
fuzes) . 

Rotor, Generator. The rotating permanent magnet 
in a generator. 

RRLG. (Rocket, Radio, Longitudinal, Generator.) An 
early designation for generator-powered proximity 
fuzes for rockets. 

Safe. The condition of a fuze which is not armed. 

SD. Self destruction. Destruction of a fuze by opera- 
tion of a device within the fuze at a predetermined 
time or distance after launching, presumably after 
the missile has passed the target. See Sections 4.3.1 
and 3.3.8. 

Sensitivity. See resistance sensitivity and Section 
3.1.2. 

Sensitivity Pattern. A hypothetical surface sur- 
rounding a missile representing the locus of target 
positions for functions. 

Serpentine. A type of single coil generator winding. 
See Section 3.4.5. 

Setback. A term referring to reaction on a fuze or 
missile caused by acceleration of the projectile. 

Signal Simulator. A laboratory device to simulate 
the signal produced by interaction of the fuze and 
target. See Section 2.12. 

Spikes. Short duration pulses, usually originating in 
triode microphonics. 

Squegging. The periodic instability of a high- 
frequency oscillator. See Section 3.1.5. 

Squib. Colloquial for electric detonator. 

Surge Current. The peak value of a thyratron plate 
current surge. 

Sylvania. Sylvania Electric Products Corporation. 


436 


GLOSSARY 


Sympathetic Function. The functioning of a fuze 
on a spurious target produced by the explosion of 
another missile. 

T. Refers to target function in a field test. 

Target Factor. Reflection coefficient of a ground tar- 
get multiplied by 100. 

Target Function. The proper function of a fuze 
upon approach to the intended target. 

Turbine. An air-driven turbine used in some models 
of generator-power fuzes. 

Vane. See windmill. 

VT. The commonly accepted designation for proximity 
fuze. It is generally understood that the letters stand 


for “variable time” but they also imply “vacuum 
tube.” 

Westinghouse. Westinghouse Electric Corporation. 

White. A code designation for 110 megacycles per 
second. 

Windmill. An externally mounted air-driven prime 
mover. 

Wurlitzer. The Rudolph Wurlitzer Corporation. 

Yellow. A code designation for 140 megacycles per 
second. 

Zenith. Zenith Radio Corporation. 

Zero Length Launcher. A launcher for rockets in 
which the rocket is supported over a negligible por- 
tion of its burning period. 



BIBLIOGRAPHY 


/ 


Numbers such as Div. 4-100-1M indicate that the document listed has been microfilmed and that its title 
appears in the microfilm index printed in a separate volume. For access to the index volume and to the 
microfilm, consult the Army or Navy agency listed on the reverse of the half-title page. 


Chapter 1 

1. ‘‘Notes on Conference of 12 August 1940 between 
representatives of NDRC and BuOrd,” by Com- 
mander C. Hoover, Aug. 17, 1940. Div. 4-100-MI 

2. “Development of Anti-Aircraft Fuzes for Rockets,” 
Initiation of Project, Ordnance Committee Min- 
utes No. 18178, Apr. 24, 1942. 

3. “Initiation of Radio Rocket Fuze Project,” Ord- 
nance Committee Minutes No. 18364, June 5, 1942. 

4. “Initiation of Development Project for T40, T43 
Fuzes,” Ordnance Committee Minutes No. 19939, 
Mar. 17, 1943. 

5. “Initiation of Development Project for T50, T51, 
T52 Fuzes,” Ordnance Committee Minutes No. 
21117, July 17, 1943. 

6. “Initiation of Development Project for T6 Fuzes,” 
Ordnance Committee Minutes No. 21681, Sept. 8, 
1943. 

7. “Initiation of Development Project for T30 Fuzes,” 
Ordnance Committee Minutes No. 25243, Sept. 28, 
1943. 

8. “Transfer of T82 Fuzes to Army Development,” 
Ordnance Committee Minutes No. 26818, Mar. 1, 
1943. 

9. “Initiation of Development Project for T32, T2005 
Fuzes,” Ordnance Committee Minutes No. 27280, 
Apr. 12, 1945. 

10. “Initiation of Development for T132, T171, T172 
Fuzes,” Ordnance Committee Minutes No. 27427, 
Apr. 26, 1945. 

11. The Optimum Point of Burst for a 500-lb GP 
Bomb Equipped with a Proximity Fuze, by 
Marston Morse, William R. Transue, Roy Kuebler, 
TDBS Report 7, Office of the Chief of Ordnance, 
Apr. 22, 1943. 

12. The Dependence of Optimum Height of Burst of 
Shells and Bombs upon Angle of Fall, Safety 
Angle, etc., by Marston Morse, William R. Tran- 
sue, TDBS Report 41, Office of the Chief of Ord- 
nance, Sept. 2, 1944. 

13. Optimum Height of Burst of Fragmentation 
Bombs and Effect with VT Fuzes, by Marston 
Morse, William R. Transue, and M. H. Heins, 
TDBS Report 58, Office of the Chief of Ordnance, 
Apr. 3, 1945. 

14. Probable Advantages of VT Fuzes on 81-mm HE 
Mortar Shell M56 and MU3A1, Marston Morse, 
William R. Transue, and M. H. Heins, TDBS Re- 
port 60, Office of the Chief of Ordnance, Mar. 30, 
1945. 

15. A Comparison of Damage Effect of Ground Bursts 
of 20-lb Bomb with an Air Burst of the 260-lb 


Bomb and of the 500-lb Bomb against Planes and 
Revetments, TDBS Report 61, Office of the Chief 
of Ordnance, Apr. 24, 1945. 

16. Second Interim Report on Fuze, Bomb, T50, Re- 
port of the Army Air Force Proving Ground Com- 
mand on Project 4012C4712.82, Apr. 12, 1945. 

17. Supplemental Tests on Aircraft Rockets for Anti- 
Personnel Effects, Report of the Army Air Forces 
Proving Ground Command on Project 4514C471.94, 
Sept. 4, 1945. 

18. Final Report on Air-to-Air Firing of Mk 171 
Mod 0 Fuzes on 3.U" and 5.0" AR, NOTS Project 
104 AFS, Aug. 5, 1945. 

19. Probability that a 1+.5" Rocket Fired from Astern 

Will Destroy a Twin-Engine Bomber (JU-88) as a 
Function of Point of Burst, AMP Report 21. 1R, 
Statistical Research Group, Applied Mathematics 
Panel, July 1944. Div. 4-412.3-MI 

20. Optimum Burst Surface for U.5" Airborne Rocket 
Fired from Astern at Twin-Engine Bomber (JU- 
88), AMP Report 21.2R, Statistical Research 
Group, Applied Mathematics Panel, July 1944. 

Div. 4-412.3-M2 

21. Effectiveness of a U.5" Airborne Rocket with T5 
Fuze When Fired at Twin-Engine Bomber from 
Astern, AMP Report 21. 3R, Statistical Research 
Group, Applied Mathematics Panel, July 1944. 

Div. 4-412.3-M3 

22. Probability' of Damage Computations Pertinent to 
Design of Fuze for 5" AR and 5" HV AR, Milton 
Friedman, Informal Study (AMP Study 21, SRG 
396), Applied Mathematics Panel, January 1945. 

Div. 4-412.3-M5 

23. Airburst for Blast Bombs, E. Bright Wilson, Jr., 

OSRD 4943, OEMsr-260 and OEMsr-569, Service 
Projects OD-03, NO-224, et al., Division 2. Report 
A-322, Princeton University, WHOI, et al., April 
1945. Div. 4-242. 12-M4 

24. Evaluation of Airburst Bombs for Clearance of 
Mine Field, Robert D. Huntoon, OSRD 4100, Serv- 
ice Project OD-27, Report A-291, September 1944. 

Div. 4-242.12-MI 

25. Effect of Height of Detonation of Bombs on the 
Blast Pressures and Impulses of Surrounding 
Buildings, in Richmond Park 1/7 Square Model 
Town Tests, Road Research Laboratory, Depart- 
ment of Scientific and Industrial Research Minis- 
try of Supply, Note MOS/434/RJ.EK, March 1945. 

26. Trials with an M6U 500-lb Bomb, Nose Initiated, 
Fuze T50 against Close Support Targets , B. L. 
Welch, Appendix to Proceeding Q-2881, Ordnance 
Board, Dec. 13, 1944. 

27. Note on Airbursts of U, 000-lb HC Bomb with T51 



437 


438 


BIBLIOGRAPHY 


Fuze , F. H. East, Technical Note ARM343, Royal 
Aircraft Establishment, April 1946. 

28. Optimum Height of Setting fo r T50 Fuze on Blast 
Bombs, A 1C LC 500-lb Mark 2 Charged Dyed 
Methyl Scelicyliate and Dropped onto Jungle, San 
Jose, Project Report 69, Chemical Warfare Serv- 
ice, June 22, 1945. 

29. Multiple Bomb Assessment of Blast Bomb A/C 
LC 500-lb Mark 2 Fitted with T51 Fuze and 
Charged HT when Dropped from High Altitudes 
into Jungle Terrain, San Jose, Project Report 73, 
Chemical Warfare Service, July 28, 1945. 

30. Interim Report, February 15 to March 7, 1945, 
A. V. Astin to Dr. Alexander Ellett. 

31. Fire Bombs Tried at Eglin Field with VT Fuzes, 
T. N. White, Report OD-2-255M, NBS, Ordnance 
Development Division, July 13, 1945. 

Div. 4-242.13-M2 

32. Operational Uses of Bomb and Rocket VT Fuzes 
by U. S. Army and Navy in World War II, Walter 
G. Finch, Report OD-Army-4, NBS, Ordnance De- 
velopment Division, Oct. 15, 1945. Div. 4-221-M2 

33. Letter to R. C. Tolman. Subject: “The Use in 
Proximity Fuzes for Rockets of the Various Elec- 
tronic Components of Small Size for Use in the 
Proximity Fuze for Antiaircraft Projectiles,” 
W. S. Parsons, May 21, 1942. Div. 4-211.1-MI 

34. Evaluation of Air Burst Bombs for Clearance of 
Mine Fields, E. F. Horton, Jr., Final Report on 
Experimental Investigation, OD-1-599, NBS, Ord- 
nance Development Division, Dec. 23, 1944. 

Div. 4-242. 12-M3 

Chapter 2 

ARMOR AND ORDNANCE REPORTS OF NDRC 

1 . Radio Controlled Antiaircraft Proximity Fuze; 
The Reflection of Radio Waves from Airplanes, 
Robert D. Huntoon, Service Project OD-27, Prog- 
ress Report A-19, Nov. 10, 1941. Div. 4-211-MI 

2. Radio Proximity Fuzes for Bombs and Rockets as 

of May 28, 1942, Harry M. Diamond, Service Proj- 
ects OD-27, OD-33, and CWS-19, Progress Report 
A-64, June 15, 1942. Div. 4-211.1-M2 

3. A Device for the Measurement of the Absolute 

Sensitivity of an End-Fed Axially -Excited Radio 
Proximity Fuze, William L. Kraushaar, and Rob- 
ert D. Huntoon, Service Project OD-27 and OD-26, 
Report A-143, Feb. 13, 1943. Div. 4-625-Ml 

4. Radio Proximity Fuze for Plane-to-Plane Rocket 
Application, Harry M. Diamond, W. S. Hinman, 
Jr., Robert D. Huntoon, Cledo Brunetti, and Ches- 
ter H. Page, Service Projects OD-27 and OD-26, 
Report A-144, Feb. 12, 1943. Div. 4-211. 1-M3 

5. VT Fuzes for Rockets and Bombs, Training Lec- 
tures, Robert D. Huntoon, Chester H. Page, B. J. 
Miller, Jacob Rabinow, and Harry M. Diamond, 
OSRD 5326, Service Projects OD-27, NO-77B, and 
NO-77R, Report A-334, January 1945. 

Div. 4-200-MI 


6. Radiation Properties of BRLG, Robert D. Huntoon, 
Service Project OD-27, Report 43-R, July 28, 1943. 

Div. 4-243. 11-Ml 

7. Design of Special Targets, Robert D. Huntoon, 
Service Project OD-27, Report 44-R, May 12, 1943. 

Div. 4-618-M2 

8 . Selection of Optimum Frequencies for BRLG 

Vehicles, Robert D. Huntoon, Service Project 
OD-27, Report 52-R, August 1943. Revised: Apr. 
17, 1944. Div. 4-243. 11-M2 

REPORTS OF ORDNANCE DEVELOPMENT DIVI- 
SION OF NATIONAL BUREAU OF STANDARDS 

9. Basic Theory of the Radio Proximity Fuze, Philip 

R. Karr, NBS, Ordnance Development Division, 
May 25, 1945. Div. 4-211-M2 

10. Afterburning from Rocket Motors and Malfunc- 
tioning of VT Fuzes (Summary Report), H. F. 
Stimson, Report OD-1-896, NBS, Ordnance De- 
velopment Division, Oct. 15, 1945. 

Div. 4-411. 11-M6 

11. Theoretical Estimates of the Radiation Resistance 
of the BRTG Propeller Antenna Model, J. G. Hoff- 
man and David Feldman, Report OD-2-30, NBS, 
Ordnance Development Division, Apr. 24, 1944. 

Div. 4-243. 21-M2 

12. Prediction of Heights of Function (Supplement 
to Report OD-3-89), Bertrand J. Miller and 
M. Schulkin, Report OD-BE-22R, NBS, Ordnance 
Development Division, Aug. 11, 1944. 

Div. 4-241-M3 

13. Electrical Interaction of T-50 Fuzes (Part II), 
Bertrand J. Miller, Report OD-BE-42R, NBS, Ord- 
nance Development Division, Sept. 29, 1944. 

Div. 4-245-M4 

14. Expected Radius of Action for the T-30 , Bertrand 
J. Miller and Franklin M. Fletcher, Report OD- 
BE-53R (and Addendum), NBS, Ordnance De- 
velopment Division, Nov. 11, 1944. 

Div. 4-241.1-MI 

15. Estimates of Radius of Action of T-30 from Steady 

State Computations, R. F. Morrison, Jr., Thomas 
M. Marion, and Franklin M. Fletcher, Report OD- 
BE-56R, NBS, Ordnance Development Division, 
Dec. 4, 1944. Div. 4-241.1-M3 

16. Construction of Apparatus for Measuring Reflec- 

tion Coefficient, Otto E. Spokas, Report OD-BE- 
77R, NBS, Ordnance Development Division, Apr. 
23, 1945. Div. 4-624-M3 

17. Measurement of the Reflection Coefficient of the 
Water Bombing Range at Aberdeen Proving 
Ground, Otto E. Spokas, Report OD-7-201R, NBS, 
Ordnance Development Division, May 1, 1945. 

Div. 4-624-M4 

18. Striking Angles and Velocities for Level Flight 
Bombing, Allen T. Foster, Report OD-7-87R, NBS, 
Ordnance Development Division, Mar. 20, 1945. 

Div. 4-311.3-M2 

19. Impact Angles and Striking Velocities for Dive 



BIBLIOGRAPHY 


/ 


439 


Bombing, F. L. Celauro, Report OD-7-88R, NBS, 
Ordnance Development Division, Mar. 22, 1945. 

Div. 4-242.14-MI 

20. Striking Angles and Velocities for Level Flight 

Bombing with the M-65 Bomb, Allen T. Foster, 
Report OD-2-223R (Supplement to OD-7-87R), 
NBS, Ordnance Development Division, June 5, 
1945. Div. 4-311.3-M3 

21. Striking Angles and Velocities for Level Flight 
Bombing with M-57, Allen T. Foster, Report OD-2- 
257R (Supplement to OD-7-87R), NBS, Ordnance 
Development Division, July 18, 1945. 

Div. 4-311.3-M4 

22. Effect of Ground Reflection on BRLG Perform- 

ance, Charles J. Apolenis and Robert D. Huntoon, 
Report OD-3-19, NBS, Ordnance Development 
Division, Nov. 2, 1943. Div. 4-243.21-MI 

23. Induction Field Sensitivity , Chester H. Page, Re- 

port OD-3-30, NBS, Ordnance Development Divi- 
sion, Nov. 16, 1943. Div. 4-233-MI 

24. Induction Field of Finite Antennas, Chester H. 

Page, Report OD-3-33, NBS, Ordnance Develop- 
ment Division, Nov. 19, 1943. Div. 4-233-M2 

25. Experimental Measurement of the Effect of an 

Imperfect Reflector on the Induction Field Sensi- 
tivity of a Radio-Proximity Fuze, Otto E. Spokas, 
Charles C. Gordon, and Robert D. Huntoon, Re- 
port OD-3-36, NBS, Ordnance Development Divi- 
sion, Nov. 25, 1943. Div. 4-624-MI 

26. Computation of Heights of Function, Including 

Induction and Quasi-Static Field Effects, Bertrand 
J. Miller and Philip R. Karr, Report OD-3-89, 
NBS, Ordnance Development Division, Jan. 29, 
1944. Div. 4-241-M2 

27. Measurement of the Reflection Coefficient of the 
New Bombing Range at Aberdeen Proving Ground, 
Otto E. Spokas, Report OD-3-90, NBS, Ordnance 
Development Division, Jan. 29, 1944. 

Div. 4-624-M2 

28. Radiation Resistance of [the M-9] Rocket, Otto 
E. Spokas, Charles C. Gordon, and Robert D. 
Huntoon, Report OD-3-105, NBS, Ordnance De- 
velopment Division, Mar. 2, 1944. 

Div. 4-243. 22-MI 

29. Microphonic Stability of Oscillator-Diode Type of 

Fuze Circuit, Robert D. Huntoon, Report OD-3- 
117, NBS, Ordnance Development Division, Mar. 
22, 1944. Div. 4-238.31-Ml 

30. Dummy Antennas, Robert D. Huntoon, Report 

OD-3-133, NBS, Ordnance Development Division, 
Apr. 20, 1944. Div. 4-233-M3 

31. Tuning Compromise for BRLG Units, Philip R. 

Karr and Otto E. Spokas, Report OD-3-139, NBS. 
Ordnance Development Division, May 2, 1944. 
Revised: June 3, 1944. Div. 4-233. 1-M5 

32. Compensated Resistors for Tuning and Loading 

Standards, E. Eisner and Paul T. Hawes, Report 
OD-3-154, NBS, Ordnance Development Division, 
May 24, 1944. Div. 4-236-M4 


33. Antenna Rings for BRLG, Philip Krupen, Report 

OD-3-162, NBS, Ordnance Development Division, 
June 15, 1944. Div. 4-233-M4 

34. RGD Field Simulator, Philip Krupen, Report OD- 

3-163, NBS, Ordnance Development Division, June 
17, 1944. Div. 4-238. 32-M7 

35. Pole Tests on Various Vehicles at Blossom Point, 
James H. Barnard, Glenn L. Scillian, and Ralph 
Stair, Report OD-3-174, NBS, Ordnance Develop- 
ment Division, Aug. 16, 1944. Div. 4-243.4-M2 

36. Radiation Patterns and Electrical Balance of 

BRTG, Glenn L. Scillian and Ralph Stair, Report 
OD-3-177, NBS, Ordnance Development Division, 
Aug. 31, 1944. Div. 4-243.11-M5 

37. Radiation Resistance of Zenith BRTG-Z Units, 

Glenn L. Scillian and Ralph Stair, Report OD-3- 
178, NBS, Ordnance Development Division, Sept. 
13, 1944. Div. 4-243. 21-M4 

38. Resonant Loading of BRTG Units by Test Boxes, 
Ralph Stair, Glenn L. Scillian, and Leonard C. 
Pochop, Report OD-3-196, NBS, Ordnance De- 
velopment Division, Nov. 13, 1944. 

Div. 4-233.1-M7 

39. Transparent Charts for Prediction of Function 
Height, Philip R. Karr, Chris Gregory, R. B. 
Schwartz, and M. L. Scott, Report OD-3-257, NBS, 
Ordnance Development Division, June 6, 1945. 

Div. 4-241-M7 

40. Low Frequency Operation of Bomb Fuzes, R. B. 
Schwartz, Report OD-3-258, NBS, Ordnance De- 
velopment Division, June 7, 1945. 

Div. 4-243. 11-Mil 

41. Computation of Burst Heights of Longitudinally - 
Excited Bomb Fuzes, R. B. Schwartz, Report OD- 
3-281, NBS, Ordnance Development Division, Aug. 

7, 1945. Div. 4-241-M8 

42. Early Functions of the MC-382 Radio-Operated 
Plane-to-Plane Rocket Fuze, Bertrand J. Miller 
and Robert D. Huntoon, Progress Report OD-3- 
AB2, NBS, Ordnance Development Division, June 

8, 1943. Div. 4-222. 128-M12 

MEMORANDA OF ORDNANCE DEVELOPMENT DI- 
VISION OF NATIONAL BUREAU OF STANDARDS 

43. Amplifier Shaping and After-Burning Pulses, 

Memorandum to Robert D. Huntoon from Ber- 
trand J. Miller, NBS, Ordnance Development Divi- 
sion, Mar. 4, 1943. Div. 4-238.212-MI 

44. After-Burning and Amplifier Shaping, Memoran- 

dum to W. S. Hinman, Jr., from Robert D. Hun- 
toon, NBS, Ordnance Development Division, Mar. 
5, 1943. Div. 4-238. 212-M2 

45. After-Burning, Memorandum to W. S. Hinman, 
Jr., from Robert D. Huntoon, NBS, Ordnance De- 
velopment Division, Mar. 18, 1943. 

Div. 4-411. 11-MI 

46. Pole Tests on British Two-Ton Vehicle, Memoran- 
dum to A. V. Astin from Ralph Stair and James 


440 


BIBLIOGRAPHY 


H. Barnard, Memorandum OD-3-33M, NBS, Ord- 
nance Development Division, Aug. 24, 1944. 

Div. 4-243.4-M3 

47. Radiation Patterns on Zenith and Westinghouse, 
BRTG, Memorandum to A. V. Astin from Ralph 
Stair Memorandum OD-3-34M, NBS, Ordnance 
Development Division, Aug. 24, 1944. 

Div. 4-243. 11-M3 

48. Computation of Expected Radius of Action, Memo- 
randum to Harry M. Diamond from Chester H. 
Page, Memorandum OD-3-53M, NBS, Ordnance 
Development Division, Nov. 6, 1944. 

Div. 4-241.1-M2 

49. Radiation Resistance of BRLG Vehicles, Memo- 
randum to Harry M. Diamond from Robert D. 
Huntoon, Memorandum OD-BE-2M, NBS, Ord- 
nance Development Division, June 20, 1944. 

Div. 4-243. 21-M3 

50. Electrical Properties of British 4, 000-lb Bomb, 
Memorandum to Alexander Ellett from Harry M. 
Diamond, Memorandum OD-BE-42M, NBS, Ord- 
nance Development Division, Aug. 26, 1944. 

Div. 4-243.1 1-M4 

51. Mutual Interaction in BRLG Units Dropped in 

Close Spaced Train, Memorandum to Harry M. 
Diamond from Bertrand J. Miller, Memorandum 
OD-BE-44M, NBS, Ordnance Development Divi- 
sion, Sept. 11, 1944. Div. 4-245-M3 

52. Radiation Properties of British U, 000-lb Bomb, 

Memorandum to Harry M. Diamond from Frank- 
lin M. Fletcher and Otto E. Spokas, Memorandum 
OD-BE-47M, NBS, Ordnance Development Divi- 
sion, Sept. 9, 1944. Div. 4-243. 11-M6 

53. Interaction Factors for BRLG Units, Memoran- 
dum to Harry M. Diamond from Franklin M. 
Fletcher, Memorandum OD-BE-48M, NBS, Ord- 
nance Development Division, Sept. 11, 1944. 

Div. 4-245-M2 

54. Radiation Properties of HVAR 5" Rocket, Memo- 

randum to Harry M. Diamond from Otto E. 
Spokas and R. F. Morrison, Jr., Memorandum OD- 
BE-50M, NBS, Ordnance Development Division, 
Sept. 13, 1944. Div. 4-243.22-M2 

55. Radiation Properties of Depth Bombs, Memoran- 

dum to Harry M. Diamond from Otto E. Spokas 
and Franklin M. Fletcher, Memorandum OD-BE- 
53M, NBS, Ordnance Development Division, Sept. 
15, 1944. Div. 4-243. 11-M7 

56. Radiation Properties of MU3 and M56, Memoran- 

dum to Harry M. Diamond from Otto E. Spokas 
and Franklin M. Fletcher, Memorandum OD-BE- 
54M, NBS, Ordnance Development Division, Sept. 
18, 1944. Div. 4-243. 13-MI 

57. Additional Measurements on Radiation Properties 
of the British U, 000-lb Bomb (Supplement to OD- 
BE-47M), Memorandum to Harry M. Diamond 
from Otto E. Spokas and Franklin M. Fletcher, 
Memorandum OD-BE-56M, NBS, Ordnance De- 
velopment Division, Sept. 19, 1944. 

Div. 4-243. 11-M8 I 


58. Radiation Properties of 1,000 and 2, 000-lb GP 

Bombs, Memorandum to Harry M. Diamond from 
Otto E. Spokas and Franklin M. Fletcher, Memo 
randum OD-BE-59M, NBS, Ordnance Development 
Division, Sept. 27, 1944. Div. 4-243.11-M9 

59. Radiation Properties of the 5-inch Mattress and 

the 155 mm Mortar Projectile, Memorandum tc 
Harry M. Diamond from Otto E. Spokas ana 
Franklin M. Fletcher, Memorandum OD-BE-63M, 
NBS, Ordnance Development Division, Sept. 30, 
1944. Div. 4-243. 13-M2 

60. Radiation Properties of Vehicles M30, M6U, and 
M81, Memorandum to Harry M. Diamond from 
Franklin M. Fletcher and Otto E. Spokas, Memo- 
randum OD-BE-66M, NBS, Ordnance Develop- 
ment Division, Oct. 5, 1944. Div. 4-243. 11-M10 

61. Calculations Concerning Radius of Action in 
Plane-to-Plane Application, Memorandum to 
Harry M. Diamond from Bertrand J. Miller, 
Memorandum OD-BE-82M, Nov. 14, 1944. 

Div. 4-412.4-M4 

62. Radiation Properties of Gas Tanks, Memorandum 
to Harry M. Diamond from Bertrand J. Miller, 
Preliminary Memorandum OD-BE-89M, NBS, 
Ordnance Development Division, Nov. 27, 1944. 

Div. 4-243.3-MI 

63. Radiation Properties of Various Rockets, Memo- 
randum to Harry M. Diamond from Bertrand J. 
Miller, Memorandum OD-BE-92M, NBS, Ord- 
nance Development Division, Dec. 12, 1944. 

Div. 4-243. 22-M3 

64. Radiation Resistance of the M56 Mortar, the MU3 
Mortar with an M56 Tail, the AN -M U1 Fragmen- 
tation Bomb and the 155 mm Chemical Mortar 
Projectile When Used with an MRLG Type Unit, 
Memorandum to Harry M. Diamond from Otto E. 
Spokas, Memorandum OD-BE/-98M, NBS, Ord- 
nance Development Division, Dec. 19, 1944. 

Div. 4-243. 23-MI 

65. The Effect of Various Antenna Rings on the Radi- 

ation Resistance of the M56 Mortar and the MU3 
Mortar with the M56 Tail, Memorandum to Harry 
M. Diamond from Otto E. Spokas, Memorandum 
OD-BE-127M, NBS, Ordnance Development Divi- 
sion, Apr. 2, 1945. Div. 4-243.23-M2 

66. Additional Radiation Resistance Data on the 

HVAR, AR3.5 and AR5 Rockets, Memorandum to 
Harry M. Diamond from Otto E. Spokas, Memo- 
randum OD-7-202M, NBS, Ordnance Development 
Division, May 1, 1945. Div. 4-243. 22-M4 

67. Radiation Resistance Presented to the Type T-2005 
Unit, Memorandum to Harry M. Diamond from 
Otto E. Spokas, Memorandum OD-7-205M, NBS, 
Ordnance Development Division, June 25, 1945. 

Div. 4-243. 22-M5 

68. Radiation Patterns of the AR and Hb.5 Rocket, 
Memorandum to Harry M. Diamond from Otto E. 
Spokas, Memorandum OD-7-212M, NBS, Ordnance 
Development Division, July 21, 1945. 

Div. 4-243. 12-M2 


/ 


BIBLIOGRAPHY 


69. Radiation Resistance of the M-56 Mortar Shell 

with 2 " Tail Extension, Memorandum to Harry M. 
Diamond from Otto E. Spokas, Memorandum OD- 
7-213M, NBS, Ordnance Development Division, 
Aug. 28, 1945. Div. 4-243.23-M3 

70. Revision and Extension of OD-OAG-20 (Striking 
Velocity, Striking Angle, Vei'tical Component of 
Striking Velocity vs Altitude), Memorandum to 
Recipients of OD-OAG-20 from D. Fisher, OD- 
OAG-41, NBS, Ordnance Development Division, 
Sept 11, 1944. 

71. Tables of Doppler Frequency vs Altitude of Re- 
lease at 200 Miles Per Hour for Carrier Fre- 
quencies, D. Fisher, Report OD-OAG-42, NBS, 
Ordnance Development Division, Sept. 19, 1944. 

Div. 4-412.4-M2 

72. Summary of Ballistic Data for the Mk-7, CIT 
Rocket, Memorandum to Harry M. Diamond from 
F. A. Ransom, Memorandum OD-OAG-45, NBS, 
Ordnance Development Division, Sept. 28, 1944. 

Div. 4-412. 4-M3 

73. Navy Rocket Trajectory Analysis, Memorandum 

to T. N. White from A. L. Leiner (in collabora- 
tion with D. C. Friedman), Memorandum OD-2- 
203, NBS, Ordnance Development Division, May 
5, 1945. Div. 4-412.1-M8 

74. Table of Bomb Velocity vs Air Travel, Allen T. 
Foster, Report OD-2-252M, NBS, Ordnance De- 
velopment Division, July 5, 1945. Div. 4-242.14-M2 

75. Striking Angles and Vertical Components of Strik- 
ing Velocities of Rockets Fired from an Airplane 
in Dive. Memorandum to T. N. White from F. L. 
Celauro, Memorandum OD-2-261M, NBS, Ord- 
nance Development Division, July 25, 1945. 

Div. 4-412. 4-M6 

REPORTS OF CONTRACTORS OF DIVISION U 
OF NDRC 

76. Research and Development Conducted by Philco 

Corporation on PU-772 Radio Proximity Fuze for 
Large Bombs (Final Report), R. A. Bell, OEMsr- 
866, Symbol 2164, Philco Radio and Television 
Corporation, June 15, 1943. Div. 4-211. 1-M4 

77. Considerations of the Problem of Adapting the 

Radio Proximity Fuze to the M-56 Mortar Pro- 
jectile, Alfred S. Khouri, University of Florida, 
Oct. 30, 1943. Div. 4-211.23-MI 

78. A Study of the Possibility of Making Both the 
Loop and Longitudinal Type Fuzes from the Basic 
University of Florida MROG Unit, Alfred S. 
Khouri, University of Florida, Apr. 3, 1945. 

Div. 4-211. 23-M5 

79. Modifications of the MROG to Reduce the Loop 
Area and Prominence of the Loop, Alfred S. 
Khouri, University of Florida, Mar. 29, 1945. 

80. Mortimer Loop Radio Proximity Fuze Report, 
University of Florida, Apr. 22, 1944. 

Div. 4-211. 23-M2 

81. Interaction of Loop Antenna and Neighboring 
Conductors with Special Reference to the MROG 

% Fuze, R. C. Williamson, Report WRL-UF-3jJJni- 
versity of Florida, Aug. 10, 1944. Div. 4-2K-M5 


441 


82. A Possible Method of Reducing the Undesired 

Parasitic Radiation from a Vehicle Excited Trans- 
versely, C. Albert Moreno, University of Florida, 

Nov. 1, 1943. Div. 4-243.4-MI 

83. Performance of the Basic MROG Design Adapted 
to End-Fed Longitudinal Excitation, Alfred S. 
Khouri, University of Florida, Apr. 12, 1945. 

84. Final Technical Report on Generator-Powered 

Proximity Fuzes for Bombs, K. D. Smith and 
A. L. Stillwell, OEMsr-905, Bell Telephone Labo- 
ratories, May 30, 1944. Div. 4-211. 21-M5 

85. Generator Report, R. N. Harmon, Westinghouse 

Electric and Manufacturing Company, Apr. 8, 
1943. Div. 4-232.2-M2 

86. Development of a Ground Approach Proximity 

Bomb Nose Fuze, BRTG, T. M. Bloomer, OEMsr- 
343 and OEMsr-1106, Termination Report CFE- 
760, Westinghouse Electric and Manufacturing 
Company, Apr. 28, 1945. Div. 4-211.21-M11 

87. Proximity Fuze, Bomb, Nose, Ground Approach, 

Type VT, T-82, T. M. Bloomer, OEMsr-343 and 
OEMsr-1106, Termination Report CFE-759, West- 
inghouse Electric and Manufacturing Company, 
Apr. 28, 1945. Div. 4-222.113-M2 

88. Proximity Fuze — Hornet, John R. Boykin, OEMsr- 

343, Termination Report CFE-762, Westinghouse 
Electric and Manufacturing Company, Apr. 28, 
1945. Div. 4-211.1-M6 

89. Proximity Fuze [ for the ] Plane-to-Plane Rocket, 
Type POD, John R. Boykin, OEMsr-343, Termina- 
tion Report CFE-761, Westinghouse Electric and 
Manufacturing Company, Apr. 28, 1945. 

Div. 4-211.1-M5 

90. BRLG Proximity Fuzes (Final Report), F. H. 
Osborne, OEMsr-1161 and OEMsr-1163, Rudolph 
Wurlitzer Company, Mar. 15, 1945. 

Div. 4-211. 22-MI 

91. Generator-Powered Radio Proximity Fuze for 
Bombs — Transverse Antenna Type, Earl J. Diehl, 
OSRD 5111, OEMsr-980 and OEMsr-1133, Service 
Projects OD-27 and NO-77B, Final Report A-326, 
Zenith Radio Corporation, Mar. 30, 1945. 

Div. 4-211.21-M10 

REPORTS OF OTHER DIVISIONS OF NDRC 

92. Repeater Jamming of Radio Proximity Fuzes, Rus- 
sell Yost, Jr., and Walter E. Tolies, OEMsr-1305, 
Service Projects SC-98.07 and NA-109, Division 15 
Report 1305-26, Jan. 27, 1946. Div. 4-246-MI 

BRITISH REPORTS 

93. Reflections from Bodies, N. F. Mott, Apr. 24, 1941. 

UNCLASSIFIED TECHNICAL PUBLICATIONS 

94. “Circuit Relations in Radiating Systems and Ap- 
plications to Antenna Problems,” P. S. Carter, 
Proceedings of the Institute of Radio Engineers, 
Vol. 20, No. 6, June 1932, pp. 1004-1041. 

95. “The Reciprocal Energy Theorem,” J. R. Carson, 
Bell System Technical Journal, Vol. 9, April 1930, 
pp. 325-331. 



442 


BIBLIOGRAPHY 


Chapter 3 

ARMOR AND ORDNANCE REPORTS OF NDRC 

1. Radio Controlled Antiaircraft Proximity Fuze: 

The Reflection of Radio Waves from Airplanes , 
Robert D. Huntoon; based on cooperative work by 
Harry M. Diamond, W. S. Hinman, Jr., Robert D. 
Huntoon, Cledo Brunetti, and Chester H. Page, 
Service Project OD-27, Progress Report A-19, 
Nov. 10, 1941. Div. 4-211-MI 

2. The Performance of Small Dry Batteries When 

Subjected to Low Temperatures and the Effect of 
Heating the Batteries Internally by Alternating 
Current Supplied to the Battery Terminals, John 
P. Schrodt, D. Norman Craig, and George W. 
Vinal, Service Project OD-27, Progress Report 
A-30, Jan. 20, 1942. Div. 4-232.1-MI 

3. The National Bureau of Standards Battery for 
Low Temperature Operation, John P. Schrodt, 
D. Norman Craig, and George W. Vinal, Service 
Project OD-27, Progress Report A-49, May 2, 1942. 

Div. 4-232.1-M2 

4. The Possibility of a Generator Power Supply for 

Proximity Fuzes, Allen S. Clarke, Service Proj- 
ects OD-27 and OD-33, Progress Report A-62M, 
Dec. 15, 1942. Div. 4-232.2-MI 

5. Radio Proximity Fuzes for Bombs and Rockets as 

of May 28, 19U2, Harry M. Diamond, Service Proj- 
ects OD-27, OD-33, and CWS-19, Progress Report 
A-64, June 12, 1942. Div. 4-211.1-M2 

6. Firing of Squibs by Condenser Discharge — Energy 
Losses in Thyratrons, Evert G. Bennett and Rich- 
ard K. Cook, Service Projects OD-27 and OD-33, 
Progress Report A-65, June 25, 1942. 

Div. 4-231. 1-MI 

7. Circuit Design of the Ultra-High Frequency Unit 

for the Radio Proximity Fuze, Chester H. Page, 
Service Projects OD-27 and OD-33, Progress Re- 
port A-80, Aug. 11, 1942. Div. 4-211. 2-MI 

8. Characteristics of Small Thyratrons for Use in 

Proximity Fuzes, Mahlon F. Peck, Service Projects 
OD-27 and OD-33, Progress Report A-112, Nov. 
10, 1942. Div. 4-231.1-M4 

9. Analysis of the Feedback Amplifier for MC-382 

Fuze, Robert D. Huntoon, William L. Kraushaar, 
and Herbert D. Cook, Progress Report A-122, 
Dec. 7, 1942. Div. 4-238.222-MI 

10. A Device for the Measurement of the Absolute 
Sensitivity of an End-Fed Axially -Ex cited Radio 
Proximity Fuze, William L. Kraushaar and Rob- 
ert D. Huntoon, Service Projects OD-27 and 
OD-26, Report A-143, Feb. 11, 1943. 

Div. 4-625-MI 

11. Radio Proximity Fuze for Plane-to-Plane Rocket 
Application, Harry M. Diamond, W. S. Hinman, 
Jr., Robert D. Huntoon, Cledo Brunetti, and Ches- 
ter H. Page, Service Projects OD-27 and OD-26, 
Report A-144, Feb. 12, 1943. Div. 4-211. 1-M3 

12. Generator Powered Radio Proximity Fuze for 


Bombs; Transverse Antenna Type, Earl J. Diehl, 
OSRD 5111, OEMsr-980 and OEMsr-1133, Service 
Projects OD-27 and NO-77B, Final Report A-326, 
Zenith Radio Corporation, Mar. 30, 1945. 

Div. 4-211. 21-M10 

13. Pilot Production of T-50 Fuzes, Allen S. Clarke 
and C. N. Julian, OSRD 5351, OEMsr-1227, Serv- 
ice Projects OD-27, NO-77B, and NO-77R, Report 
A-335, Bowen and Company, Inc., Apr. 12, 1945. 

Div. 4-222. 111-M3 

14. A Radio Proximity Fuze: Type MROG, OSRD 

5412, OEMsr-949, Service Project OD-27, Report 
A-338, War Research Laboratory, University of 
Florida, April 1945. Div. 4-211.23-M3 

15. Specification for Rectifier Bridge Assembly RA-1, 

NBS, Ordnance Development Division, July 5, 
1944. Div. 4-235-M6 

16. Specification of Generator G-l, NBS, Ordnance 
Development Division, Dec. 9, 1944. 

Div. 4-232. 2-M20 

17. Specification of Power Supply PS-1 and PS-2, 

NBS, Ordnance Development Division, Dec. 9, 
1944. Div. 4-232.2-21 

NDRC ENGINEERING REPORTS 

18. Status Report on Design of Generator-Powered 
Radio Fuze, Chester H. Page and F. Stanley 
Atchison, Service Projects OD-27 and SC-40, 
Engineering Report 1-R, May 29, 1943. 

Div. 4-211.2-M2 

19. Status of Generator Development, George V. 
Morris, Service Project OD-27, Engineering Re- 
port 3-R, Zenith Radio Corporation, May 27, 1943. 

Div. 4-232. 2-M6 

20. Preliminary Discussion of Amplifier Simplification 
For MC-382 Fuze, R. H. Pintell, Service Project 
OD-27, Memorandum Report 35-R, Emerson Radio 
and Phonograph Corporation, Apr. 8, 1943. 

Div. 4-238. 222-M2 

21. Status of Generator Development, R. N. Harmon, 

Service Project OD-27, Memorandum Report 38-R, 
Westinghouse Electric and Manufacturing Com- 
pany, Apr. 8, 1943. Div. 4-232.2-M3 

22. Generator Regulation, Chester H. Page, Service 

Project OD-27, Memorandum Report 40-R, Apr. 
26, 1943. Div. 4-232.2-M4 

23. Amplifier Specifications for MC-382 Fuze, R. H. 

Pintell, Service Project OD-27, Parts I and II, 
Memorandum Report 48-R, Emerson Radio and 
Phonograph Corporation, May 24 and July 24, 
1943. Div. 4-238.222-M3 

REPORT OF ORDNANCE DEVELOPMENT 
DIVISION OF NATIONAL BUREAU 
OF STANDARDS 

24. Leakage Resistance of BS-U and BS-5 Detonators, 
W. A. Yates, Report OD-1-75, NBS, Ordnance De- 
velopment Division, Dec. 4, 1943. 

Div. 4-238.523-MI 





BIBLIOGRAPHY 443 


25. BS-4 Detonators Fired through Sylvania SA-782-B 
Thyratrons, Summary Report on Recent Tests, G. 
Singer and T. N. White, Report OD-1-82, NBS, 
Ordnance Development Division, Dec. 21, 1943. 

Div. 4-238. 521-M6 

26. Time Lags in BS-1* Detonators When Fired with- 

out Firing Condensers, L. C. Miller, Report OD-1- 
154, NBS, Ordnance Development Division, Feb. 
15, 1944. Div. 4-238. 521-M8 

27. BRLG Generator Speeds for Several Combinations 
of Vehicle, Propeller Lead, and Manufacturer, 
D. C. Friedman, Report OD-1-256 and 256A 
(Supplement), NBS, Ordnance Development Di- 
vision, May 22, 1944 and June 6, 1944. 

Div. 4-232. 2-M14 (Supp.), Div. 4-232.2-M13 

28. Field Test — 27 Philco T50E1 with Metal Pro- 
pellers (PX-5), D. A. Worcester and D. C. Fried- 
man, Report OD-1-405, NBS, Ordnance Develop- 
ment Division, July 17, 1944. Div. 4-222. 111-MI 

29. Field Test — 1*0 Bowen T50E10 Units Lot 11*1 (CB- 

1*20), E. F. Horton and R. Vorkink, Report OD-1- 
585, NBS, Ordnance Development Division, Dec. 
14, 1944. Div. 4-222. 111-M2 

30. Field Test — 21 Zenith T51 Units, Lot 53, (CB- 

1*30), D. A. Worcester and G. Rabinow, Report 
OD-1-626, NBS, Ordnance Development Division, 
Jan. 19, 1945. Div. 4-222.112-MI 

31. Field Test — Philco T50E1 Reporters with Dough- 

nut Arming Ring, D. W. Scott, Report OD-1-660, 
NBS, Ordnance Development Division, Feb. 22, 
1945. Div. 4-222. 127-M2 

32. Lot Quality Test of 12 Philco T-30 Units (TBG- 

95), R. G. Tobey and G. Rabinow, Report OD-1- 
664, NBS, Ordnance Development Division, Mar. 2, 
1945. Div. 4-222. 124-M2 

33. High Altitude Test, 21* Zenith T-51 Units (CB- 

1*57), D. A. Worcester and G. Rabinow, Report 

OD-1-684, NBS, Ordnance Development Division, 
Mar. 24, 1945. Div. 4-222.112-M2 

34. BS-5 Detonators Fired with 1.5 Microfarad Con- 
denser, Charles C. Gordon, Report OD-1-699, NBS, 
Ordnance Development Division, Apr. 2, 1945. 

Div. 4-238.522-M3 

35. High Altitude Test — 12 Zenith T-51 Units (CB- 

1*61*), D. A. Worcester and G. Rabinow, Report 
OD-1-701, NBS, Ordnance Development Division, 
Apr. 12, 1945. Div. 4-222.112-M3 

36. Arming Test — 18 Westinghouse T-82 Units (CB- 

1*71*), D. A. Worcester and G. Rabinow, Report 
OD-1-715, NBS, Ordnance Development Division, 
Apr. 19, 1945. Div. 4-222.113-MI 

37. Field Test — 20 Westinghouse T-82 Units (CB- 

1*73), D. A. Worcester and R. Vorkink, Report 
OD-1-733, NBS, Ordnance Development Division, 
May 8, 1945. Div. 4-222.113-M3 

38. Field Test — 20 Westinghouse T-82 Units (CB- 

1*79), D. A. Worcester and R. Vorkink, Report 
OD-1-736, NBS, Ordnance Development Division, 
May 8, 1945. Div. 4-222.113-M4 


39. Field Test — 21 Zenith T-51 Units (CB-1*81), R. 
Vorkink, Report OD-1-749, NBS, Ordnance De- 
velopment Division, May 18, 1945. 

Div. 4-222. 112-M4 

40. Field Test — 18 Emerson T-92 Units (CB-1*82), 

D. A. Worcester and R. Vorkink, Report OD-1-755, 
NBS, Ordnance Development Division, May 21, 
1945. Div. 4-222. 114-MI 

41. 73 — Globe Union T-132 (CHP-1*3) , R. G. Tobey 
and D. C. Friedman, Report OD-1-763, NBS, 
Ordnance Development Division, June 4, 1945. 

Div. 4-222.131-M3 

42. Reporter Test — 10 Westinghouse T-82E1 Units 

(BX-12), D. A. Worcester and G. Rabinow, Report 
OD-1-879, NBS, Ordnance Development Division, 
Aug. 28, 1945. Div. 4-222.113-M5 

43. A Two-Stage Feedback Amplifier, Ralph Stair, 
Thomas M. Marion, and E. Eisner, Report OD-2-6, 
NBS, Ordnance Development Division, Nov. 24, 

1943. Div. 4-238. 227-MI 

44. Regulation with Non-Linear Resistors in Series 
with Load Current, J. G. Hoffman, Report OD-2-7, 
NBS, Ordnance Development Division, Jan. 1, 

1944. Div. 4-236-M2 

45. Investigation of Design Features of Westinghouse 
MK Generators, J. G. Reid, Jr., and Charles 
Ravitsky, Report OD-2-20, NBS, Ordnance De- 
velopment Division, Feb. 23, 1944. 

Div. 4-232. 2-M12 

46. Two-Tube Amplifier for BRTG-Pl*B Audio Am- 

plifier, Ralph Stair and Thomas M. Marion, Report 
OD-2-33, NBS, Ordnance Development Division, 
May 13, 1944. Div. 4-238.226-MI 

47. BRTG-P1*C Amplifier, Ralph Stair and Thomas M. 
Marion, Report OD-2-38, NBS, Ordnance De- 
velopment Division, June 7, 1944. 

Div. 4-238.226-M2 

48. Arming of VT Bomb Fuzes, A. L. Leiner, Report 

OD-2-275, NBS, Ordnance Development Division, 
Sept. 15, 1945. Div. 4-244.1-M3 

49. Pentode Acceptance Amplifier, Robert D. Huntoon, 

Report OD-BE-1, NBS, Ordnance Development 
Division, June 19, 1944. Div. 4-238.227-M3 

50. Comparison of Radiated Power of OD and RGD 

Oscillators, R. F. Morrison, Jr., Report OD-BE- 
7R, NBS, Ordnance Development Division, July 
17, 1944. Div. 4-238.3-M2 

51. Comparison of OD and RGD Circuits, R. B. 
Schwartz, Report OD-BE-13R, NBS, Ordnance 
Development Division, July 29, 1944. 

Div. 4-238.3-M3 

52. Voltage Relationships in the RGD Oscillator, R. F. 
Morrison, Jr., Report OD-BE-30R, NBS, Ordnance 
Development Division, Aug. 23, 1944. 

Div. 4-238. 32-M9 

53. Measurement of BRTG Sensitivity , R. F. Morrison, 

Jr., Report OD-BE-39R, NBS, Ordnance Develop- 
ment Division, Sept. 18, 1944. Div. 4-625-M2 

54. ^ Delay of 10-E Amplifier, R. B. Schwartz, Report 


444 


BIBLIOGRAPHY 


OD-BE-41R, NBS, Ordnance Development Di- 
vision, Sept. 25, 1944. Div. 4-238.223-M3 

55. A High Gain Amplifier Employing a Twin Triode 

Tube, Thomas M. Marion, Report OD-BE-47R, 
NBS, Ordnance Development Division, Oct. 18, 
1944. Div. 4-231.3-M3 

56. Probability Distribution of Arming Time Using 

RC Arming, Charles Ravitsky, Report OD-BE- 
49R, NBS, Ordnance Development Division, Oct. 
23, 1944. Div. 4-238.514-M3 

57. Analysis of the BS4 Detonator, Charles Ravitsky, 

Report OD-BE-73R, NBS, Ordnance Development 
Division, Mar. 7, 1945. Div. 4-238. 521-M9 

58. The Detonator Circuit, Charles Ravitsky, Report 

OD-BE-74R, NBS, Ordnance Development Di- 
vision, Mar. 7, 1945. Div. 4-238. 523-M4 

59. Measurement of Firing Voltage, Robert D. 

Huntoon, NBS, Ordnance Development Division, 
Aug. 20, 1943. Div. 4-621-M2 

60. Gain Control for Amplifiers, Robert D. Huntoon 

and F. Lamar Cooke, NBS, Ordnance Development 
Division, Aug. 23, 1943. Div. 4-238.211-MI 

61. Preliminary Information on Audio Amplifier for 

BRLG-10, Robert D. Huntoon and F. Lamar 
Cooke, NBS, Ordnance Development Division, 
Sept. 18, 1943. Div. 4-238.222-M4 

62. Status Report on Rectifier Sub Group, F. Stanley 
Atchison, Report OD-3-I, NBS, Ordnance De- 
velopment Division, Aug. 11, 1943. 

Div. 4-235-MI 

63. Tolerances on Complete BRLG-8, Robert D. 
Huntoon, Report OD-3-6a, NBS, Ordnance De- 
velopment Division, Oct. 22, 1943. Div. 4-211. 21-Ml 

64. Performance of Westinghouse AQ Copper Oxide 

Rectifying Cells, F. Stanley Atchison, Report OD- 
3-VII, NBS, Ordnance Development Division, Aug. 
24,1943. Div. 4-235-M2 

65. Effect of Static Characteristics of Rectifier Cells 

on A and B Voltages, F. Stanley Atchison, Report 
OD-3-IX, NBS, Ordnance Development Division, 
Sept. 15, 1943. Div. 4-235-M3 

66. Critical Grid Voltage of Thyratron and Hum 

Voltage Output of BRLG-11, F. Lamar Cooke, Re- 
port OD-3-9, NBS, Ordnance Development Di- 
vision, Oct. 27, 1943. Div. 4-231. 1-M7 

67. Methods of Measuring the Critical Voltage of 

Thyratrons, F. Lamar Cooke, Report OD-3-13, 
NBS, Ordnance Development Division, Nov. 9, 
1943. Div. 4-231. 1-M8 

68. Generator Performance, William L. Kraushaar, 

Report OD-3-17, NBS, Ordnance Development 
Division, Nov. 1, 1943. Div. 4-232.2-M8 

69. Performance of Power Supply at High and Low 

Temperatures, F. Stanley Atchison, Report OD- 
3-23, NBS, Ordnance Development Division, Nov. 
6, 1943. Div. 4-232.2-M9 

70. BRLG-11 A Amplifier for Zell Manufacture, Robert 
D. Huntoon, Report OD-3-24, NBS, Ordnance De- 
velopment Division, Nov. 8, 1943. 

Div. 4-238.224'-Ml 


71. Amplifier Performance of BRLG-8 Potted with 
Glidden Compound, Albert Weiss, Report OD-3-26, 
Nov. 8, 1943, and OD-3-26a, Nov. 18, 1943, NBS, 
Ordnance Development Division, Nov. 8, 1943. 

Div. 4-239.1-M4 

72. Experiments with Standard MC-382 Fuzes Con- 

verted to Reaction Type Fuzes with Grid Detection 
(RGD Fuze), Philip Krupen and W. S. Hinman, 
Jr., Report OD-3-27, NBS, Ordnance Development 
Division, Nov. 15, 1943. Div. 4-238. 32-MI 

73. Discussion of Proposed Rectifier Specifications, 
F. Stanley Atchison, Report OD-3-28, NBS, Ord- 
nance Development Division, Nov. 6, 1943. 

Div. 4-235-M5 

74. Preliminary Report on Tuning and Loading De- 

vices for BRLG, Paul E. Landis, Report OD-3-37, 
NBS, Ordnance Development Division, Nov. 29, 
1943. Div. 4-233.1-MI 

75. New Amplifier Design, Robert D. Huntoon, Re- 

port OD-3-38, NBS, Ordnance Development Di- 
vision, Nov. 29, 1943. Div. 4-238.213-MI 

76. Component Specifications for BRLG-11 A, Robert 
D. Huntoon, Report OD-3-39, NBS, Ordnance De- 
velopment Division, Dec. 2, 1943. 

Div. 4-238. 224-M2 

77. Design and Tolerance Curves for BRLG-11 A, F. 

Lamar Cooke and Robert D. Huntoon, Report 
OD-3-40, NBS, Ordnance Development Division, 
Dec. 3, 1943. Div. 4-238.224-M3 

78. Effect of Component Tolerances on Performance 

of BRLG-11 A, Robert D. Huntoon, Report OD- 

3-46, NBS, Ordnance Development Division, Dec. 
7, 1943. Div. 4-238. 224-M4 

79. Report on Status of Work on RGD, Bertrand J. 
Miller, Report OD-3-47, NBS, Ordnance Develop- 
ment Division, Dec. 7, 1943. Div. 4-238.32-M2 

80. Experiments with the RGD Circuit, Applied to 

BRLG-8, William L. Kraushaar, Report OD-3-48, 
NBS, Ordnance Development Division, Dec. 9, 
1943. Div. 4-238.32-M3 

81. Status of BRLG Production Designs, W. S. Hin- 
man, Jr., Report OD-3-57, NBS, Ordnance De- 
velopment Division, Dec. 16, 1943. 

Div. 4-211. 21-M3 

82. Effect of Tolerances in the Regulation Networ'k, 
William L. Kraushaar, Report OD-3-60, NBS, 
Ordnance Development Division, Dec. 17, 1943. 

Div. 4-232. 2-M10 

83. Performance of Zell 11 A Amplifiers on Standard 

Test Voltages, Robert D. Huntoon, Report OD-3-63, 
NBS, Ordnance Development Division, Dec. 23, 
1943. Div. 4-238. 224-M5 

84. Arming Considerations in T6, Bertrand J. Miller 
and Philip R. Karr, Report OD-3-74, NBS, Ord- 
nance Development Division, Jan. 22, 1944. 

Div. 4-238.515-MI 

85. An RGD Circuit for the MC-382, Philip Krupen, 

Report OD-3-79, NBS, Ordnance Development Di- 
vision, Jan. 15, 1944. Div. 4-238.32-M4 

86. BRLG-10 A, F. Lamar Cooke, Report OD-3-94, 


BIBLIOGRAPHY 


445 


NBS, Ordnance Development Division, Feb. 3, 
1944. Div. 4-238.227-M2 

87. Arming Resistor for T5, Robert D. Huntoon, Re- 

port OD-3-101, NBS, Ordnance Development Di- 
vision, Feb. 22, 1944. Div. 4-236-M3 

88. RGD Circuit for BRLG Applications, Philip 
Krupen, Report OD-3-102, NBS, Ordnance De- 
velopment Division, Feb. 24, 1944. 

Div. 4-238.32-M5 

89. Amplifier Characteristics for T6 Application, 

Charles J. Apolenis and Robert D. Huntoon, Re- 
port OD-3-107, NBS, Ordnance Development Di- 
vision, Mar. 7, 1944. Div. 4-238. 225-MI 

90. Microphonic Stability of the Oscillator-Diode Type 

of Fuze Circuit, Robert D. Huntoon, Report OD- 
3-117, NBS, Ordnance Development Division, Mar. 
22, 1944. Div. 4-238.31-MI 

91. Dummy Antennas, Robert D. Huntoon, Report OD- 

3-133, NBS, Ordnance Development Division, Apr. 
20, 1944. Div. 4-233-M3 

92. MRLG Apex Firing and Generator Regulation, 
Chester H. Page, Report OD-3-142, NBS, Ord- 
nance Development Division, May 9, 1944. 

Div. 4-512-MI 

93. Linearity of 11 A Amplifier, George Nordquist, Re- 

port OD-3-148, NBS, Ordnance Development Di- 
vision, May 13, 1944. Div. 4-238.224-M6 

94. Uniformity of Raytheon Triodes in RGD, Chester 
H. Page, Report OD-3-149, NBS, Ordnance De- 
velopment Division, May 13, 1944. Div. 4-231. 3-MI 

95. Triode Microphonics, Robert D. Huntoon, Bert- 

rand J. Miller, and R. B. Schwartz, Report OD-3- 
153, NBS, Ordnance Development Division, May 
20, 1944. Div. 4-231.3-M2 

96. Behavior of the 11 A Amplifier at 5,000 CPS, Philip 

R. Karr and George Nordquist; Report OD-3-156, 
NBS, Ordnance Development Division, May 25, 
1944. Div. 4-238. 224-M7 

97. Amplifier Hum Suppression, Robert D. Huntoon, 
and Philip R. Karr, Report OD-3-158, NBS, Ord- 
nance Development Division, June 9, 1944. 

Div. 4-238.213-M2 

98. Voltage Speed Regulation of Zenith Generators, 

Morris Brenner and Ralph L. Ueberall, Report 
OD-3-167, NBS, Ordnance Development Division, 
July 1, 1944. Div. 4-232.2-M15 

99. Effect of Low Temperature and High Voltage on 
Performance of 11 A Amplifier, Philip R. Karr 
and Milton Weiss, Report OD-3-169, NBS, Ord- 
nance Development Division, July 19, 1944. 

Div. 4-238.224-M8 

100. 10E Amplifier, Philip R. Karr and Chester H. 
Page, Report OD-3-170, NBS, Ordnance Develop- 
ment Division, July 21, 1944. Div. 4-238.223-MI 

101. Effect of Amplifier Shape on Function Height of 
T50 E10, Philip R. Karr, Report OD-3-172, NBS, 
Ordnance Development Division, Aug. 11, 1944. 

Div. 4-238.223-M2 

102. Effect of Potting Upon Amplifier Shaping, Philip 
R. Karr and George Nordquist, Report OD-3-175, 


NBS, Ordnance Development Division, Aug. 17, 
1944. Div. 4-239.1-M5 

103. Component Tolerance Study on BRTG-P5 Am- 

plifier, Chris Gregory and Ralph Stair, Report 
OD-3-180, NBS, Ordnance Development Division, 
Sept. 22, 1944. Div. 4-238.226-M3 

104. Effect of Low Plate Supply Voltage on RGD-PB 

Units, Philip Krupen and Leonard C. Pochop, Re- 
port OD-3-184, NBS, Ordnance Development Di- 
vision, Oct. 6, 1944. Div. 4-238.32-M10 

105. Universal High Gain Amplifier, George Nordquist, 

Report OD-3-186, NBS, Ordnance Development 

Division, Oct. 20, 1944. Div. 4-238.211-M3 

106. The Performance of Zenith BRTG-Z Units as 
Function of Supply Voltages, Lawrence J. Diou 
and Ralph Stair, Report OD-3-189, NBS, Ord- 
nance Development Division, Oct. 27, 1944. 

Div. 4-621-M3 

107. Tube and Component Study of 10E Amplifier, 
Chris Gregory, Report OD-3-190, NBS, Ordnance 
Development Division, Oct. 30, 1944. 

Div. 4-238. 223-M4 

108. Test of Four Types of Power Supplies and Gen- 
erators (Quam Nichols, Utah, Knapp-Monarch 
and Wurlitzer), Ralph L. Ueberall, Report OD-3- 

193, NBS, Ordnance Development Division, Nov. 

9, 1944. Div. 4-232.2-M18 

109. Experimental Production of High Gain Modified 
White Amplifiers, Philip R. Karr, Report OD-3- 

194, NBS, Ordnance Development Division, Nov. 

8, 1944. Div. 4-238.211-M4 

110. Use of Off -Tolerance Condensers in the 10E Am- 
plifier, George Nordquist, Report OD-3-195, NBS, 
Ordnance Development Division, Nov. 11, 1944. 

Div. 4-237-M5 

111. Sensitivity of BRTG-POD, Glenn L. Scillian and 
Chester H. Page, Report OD-3-199, NBS, Ord- 
nance Development Division, Nov. 17, 1944. 

Div. 4-238.31-M2 

112. Alteration of Feedback Components in the Basic 

10E Circuit, George Nordquist, Report OD-3-200, 
NBS, Ordnance Development Division, Nov. 18, 
1944. Div. 4-238.223-M5 

113. Electrical Design Considerations for T-30, William 

E. Kraushaar, R. B. Schwartz, and Bertrand J. 
Miller, Report OD-3-203, NBS, Ordnance Develop- 
ment Division, Dec. 5, 1944. Div. 4-241-M4 

114. The BRTG-T1B Amplifier, Ralph Stair and Glenn 
L. Scillian, Report OD-3-204, NBS, Ordnance De- 
velopment Division, Dec. 7, 1944. 

Div. 4-238.225-M2 

115. Proposed Amplifier for T-30 (Air-to-Ground, Air- 
to-Air), Philip R. Karr, Report OD-3-205, NBS, 
Ordnance Development Division, Dec. 12, 1944. 

Div. 4-238. 225-M3 

116. The 11-N2 Medium Band Amplifier, George Nord- 
quist, Report OD-3-208, NBS, Ordnance Develop- 
ment Division, Jan. 8, 1945. Div. 4-238. 227-M4 

117. Plate Voltage Fluctuations of Generator Power 
Supplies, James H. Barnard, Leonard C. Pochop, 


SECRET 


446 


BIBLIOGRAPHY 


and Ralph Stair, Report OD-3-210, NBS, Ord- 
nance Development Division, Jan. 22, 1945. 

Div. 4-232. 2-M22 

118. An RGD Oscillator for Working into High Radia- 

tion Resistances , Richard F. Mills, Report OD-3- 
212, NBS, Ordnance Development Division, Jan. 
24, 1945. Div. 4-238.32-M11 

119. Use of T-30 Filter with Wurlitzer Generator, 
Chester H. Page, Report OD-3-214, NBS, Ord- 
nance Development Division, Jan. 31, 1945. 

Div. 4-237-M6 

120. T-50 Function Height for Various Amplifiers 

under Manifold Release Conditions, Mary L. Scott, 
Report OD-3-215, NBS, Ordnance Development 

Division, Feb. 2, 1945. Div. 4-241-M5 

121. A Simplified RGD-PB Oscillator, Paul Miller, Re- 

port OD-3-216, NBS, Ordnance Development Di- 
vision, Feb. 7, 1945. Div. 4-238.32-M12 

122. Revised Circuit for BRTG-TlB Amplifier, Dorothy 

R. Adams and George Nordquist, Report OD-3- 
219, NBS, Ordnance Development Division, Mar. 
2, 1945. Div. 4-238.225-M5 

123. The T-132 (mortar fuze) Apex Performance Prob- 

lem, William L. Kraushaar, Report OD-3-220, 
NBS, Ordnance Development Division, Mar. 3, 
1945. Div. 4-222.131-M2 

124. Selection of Screen Grid Voltage Divider for 

MRLG-1, T-132 , in Connection with the Apex Fir- 
ing Problem, George Nordquist, Report OD-3-221, 
NBS, Ordnance Development Division, Mar. 10, 
1945. Div. 4-512-M2 

125. Temperature Coefficient of Allen-Bradley , Erie, 

Continental Carbon % Watt Resistors, and IRC 
X A Watt Resistors, F. W. Jirauch, Report OD-3- 
222, NBS, Ordnance Development Division, Mar. 
2, 1945. Div. 4-236-M11 

126. Frequency Modulation in Generators, Ralph Stair 
and Glenn L. Scillian, Report OD-3-223P, NBS, 
Ordnance Development Division, Mar. 12, 1945. 

Div. 4-232. 2-M23 

127. Suggested Amplifier for T-132L Having Low Gain 

at Low Frequency, George Nordquist, Report OD- 
3-225, NBS, Ordnance Development Division, Mar. 
12, 1945. Div. 4-238.225-M6 

127a. The RGD Oscillator, Philip Krupen, Report 

OD-3-227, NBS, Ordnance Development Di- 
vision, Mar. 14, 1945. Div. 4-238.32-M13 

128. The Effect of Tube Parameters on the Available 
Gain of Amplifiers, Chris Gregory, Report OD-3- 

231, NBS, Ordnance Development Division, Mar. 

17, 1945. Div. 4-238.211-M5 

129. A Quasi-Hartley Plate-Loaded RGD Oscillator, 

Paul Miller and Richard F. Mills, Report OD-3- 

232, NBS, Ordnance Development Division, Mar. 

20, 1945. Div. 4-238.32-M14 

130. Preliminary Report on Heights of Function with 

Proposed Universal Amplifier for Mortar Applica- 
tion, Philip R. Karr, Mary L. Scott, and George 


Nordquist, Report OD-3-235P, NBS, Ordnance De- 
velopment Division, Apr. 4, 1945. Div. 4-241-M6 

131. Addendum to OD-3-235P, George Nordquist, April 

16, 1945. Div. 4-241-M6 

132. Comparison of Wire-Wound and Ceramic Gain 

Controls for Use in the 10E Amplifier, F. W. 
Jirauch and Donald G. Green, Preliminary Re- 
port OD-3-236P, NBS, Ordnance Development Di- 
vision, Apr. 7, 1945. Div. 4-238.211-M6 

133. Apex Performance of the T-171 Mortar Fuze with 

RC Arming Delay, Philip Krupen, Report OD-3- 
242, NBS, Ordnance Development Division, May 
5, 1945. Div. 4-238.514-M4 

134. Thyratron Normal Critical Voltages for Various 

Amplifiers, George Nordquist, Report OD-3-249, 
NBS, Ordnance Development Division, May 24, 
1945. Div. 4-231. 1-M11 

135. Temperature Effect on G-U T-132 Amplifiers and 
Amplifier Components, F. W. Jirauch and Donald 
G. Green, Preliminary Report OD-3-252P, NBS, 
Ordnance Development Division, May 28, 1945. 

Div. 4-238.225-M8 

136. Response of Shaped Amplifiers to Step Pulses and 
Sharp Pulses, Philip R. Karr, R. B. Schwartz, and 
Mary L. Scott, Report OD-3-253, NBS, Ordnance 
Development Division, May 31, 1945. 

Div. 4-238.212-M4 

137. Pentode Input Impedance, George Nordquist, Re- 

port OD-3-254, NBS, Ordnance Development Di- 
vision, May 31, 1945. Div. 4-231.4-M12 

138. Temperature Characteristics of the Ceramic Con- 
densers in the Globe-Union T-132 Amplifier, F. W. 
Jirauch, Report OD-3-255P, NBS, Ordnance De- 
velopment Division, June 4, 1945. Div. 4-237-M9 

139. Grid Bias Circuit for T-171 Mortar Fuze to Re- 
duce Apex Malfunction, George Nordquist and 
Dorothy R. Adams, Report OD-3-256, NBS, Ord- 
nance Development Division, June 5, 1945. 

Div. 4-238.514-M5 

140. Transparent Charts for Prediction of Function 

Height, Philip R. Karr, Chris Gregory, R. B. 
Schwartz, and Mary L. Scott, Report OD-3-257, 
NBS, Ordnance Development Division, June 6, 
1945. Div. 4-241-M7 

141. Revised T-2005 Amplifier, Dorothy R. Adams, Re- 

port OD-3-264, NBS, Ordnance Development Di- 
vision, July 30, 1945. Div. 4-238.225-M9 

142. A Study of Some Amplifier Curves for Use with 
the MU3C Mortar, Mary L. Scott and George Nord- 
quist, Report OD-3-267P, NBS, Ordnance De- 
velopment Division, July 4, 1945. 

Div. 4-238. 213-M3 

143. Correlation of Rotor Magnetic Characteristics 
with Generator Output, Glenn L. Scillian and 
Ralph L. Ueberall, Report OD-3-269, NBS, Ord- 
nance Development Division, July 5, 1945. 

Div. 4-232. 22-M9 

144. Effect of Key Components on Amplifier Response 
Characteristics, George Nordquist, Report OD-3- 


BIBLIOGRAPHY 


447 


275, NBS, Ordnance Development Division, July 
16, 1945. Div. 4-238.213-M4 

145. Air Speed-Generator Output Regulation for Mor- 
tar Shell Fuzes , Glenn L. Scillian and L. M. An- 
drews, Report OD-3-278, NBS, Ordnance Develop- 
ment Division, July 20, 1945. Div. 4-232. 2-M25 

146. Arming Pulse Protection Circuit. Philip R. Karr, 

William L. Kraushaar, and Chester H. Page, Re- 
port OD-3-284, NBS, Ordnance Development Divi- 
sion, Sept. 14, 1945. Div. 4-238.515-M6 

147. Effect of Different Regulation Networks on T-132 

Generator Speeds, Glenn L. Scillian, Report OD- 
3-286, NBS, Ordnance Development Division, Sept. 
14, 1945. Div. 4-232. 2-M26 

148. Generator Voltage Measurements, F. Manov and 

Jacob Rabinow, Report OD-4-1, NBS, Ordnance 
Development Division, Aug. 13, 1943. 

Div. 4-621-MI 

149. Absolute Frictional Torque of Generator Bearings, 
A. Chartock and L. B. Heilprin, Report OD-4-7, 
NBS, Ordnance Development Division, Nov. 29, 

1943. Div. 4-232.23-MI 

150. Speed Regulating Propellers, Jacob Rabinow, Re- 

port OD-4-11, NBS, Ordnance Development Divi- 
sion, Dec. 4, 1943. Div. 4-232.21-MI 

151. Specification of Maximum Starting Torque of 

Complete BRLG Unit, A. Chartock and L. B. Heil- 
prin, Report OD-4-13, NBS, Ordnance Develop- 
ment Division, Dec. 6, 1943. Div. 4-211.21-M2 

152. Propeller Torque at Low Velocity, L. M. Andrews, 

Report OD-4-19, NBS, Ordnance Development Di- 
vision, Dec. 21, 1945. Div. 4-232.21-M3 

153. Bursting Speed of Generator Rotors, Samuel 
Kolodny, Report OD-4-6, NBS, Ordnance Develop- 
ment Division, Feb. 23, 1944. Div. 4-232.22-M4 

154. Measurement of Dynamic Propeller Unbalance, 
E. U. Rotor and L. G. Koontz, Report OD-4-43, 
NBS, Ordnance Development Division, Mar. 23, 

1944. Div. 4-232. 21-M5 

155. Comparative Speeds of Brass and Bakelite Pro- 

pellers (Supp. 1), Louis Schuman, Report OD-4-45, 
NBS, Ordnance Development Division, Apr. 6, 
1944. Div. 4-232. 21-M6 

156. Propeller Unbalance Tester (3 supplements), 
Jacob Rabinow, Report OD-4-48, NBS, Ordnance 
Development Division, Apr. 20, 1944. 

Div. 4-616-MI 

157. Torque Developed by 2"xl2" RRLG Propellers, 

Samuel Kolodny, Report OD-4-51, NBS, Ordnance 
Development Division, Apr. 19, 1944. 

Div. 4-232. 21-M7 

158. Speed Tests of Stamped Brass and Duralumin 

Propellers (3 supplements), Louis Schuman, Re- 
port OD-4-60, NBS, Ordnance Development Divi- 
sion, May 22, 1944. Div. 4-232.21-M8 

159. Life Test on Oilite Bearings of MRLG Units, 
A. Chartock, Report OD-4-74, NBS, Ordnance De- 
velopment Division, June 16, 1944. 

Div. 4-232. 23-M3 


160. Determination of Static Thrust Load Limit for the 
V 2 Inch New Departure R-3 Ball Bearing, A. Char- 
tock, Report OD-4-83, NBS, Ordnance Develop- 
ment Division, Sept. 19, 1944. Div. 4-232. 23-M4 

161. The Use of Precision Bearings in BRLG and T-50 
Noses, Jacob Rabinow, Report OD-4-88, NBS, Ord- 
nance Development Division, Dec. 14, 1944. 

Div. 4-232.23-M6 

162. Fifty Indiana Steel and Arnold Engineering 
Rotors Submitted for Test by Bowen and Com- 
pany, Samuel Kolodny, Report OD-4-97, NBS, 
Ordnance Development Division, Mar. 2, 1945. 

Div. 4-232.22-M6 

163. Effect of Condenser Leakage on RC Arming, Cledo 
Brunetti, Report OD-5-126, NBS, Ordnance De- 
velopment Division, Sept. 23, 1943. 

Div. 4-238.514-MI 

164. Noise Performance of Raytheon Diodes, M. Schul- 

kin, Report OD-5-224, NBS, Ordnance Develop- 
ment Division, Dec. 7, 1943. Div. 4-231. 2-MI 

165. Surge Current Performance and Requireme?its of 

BRLG Filter Condensers, Willis E. Armstrong, 
Report OD-5-594, NBS, Ordnance Development 
Division, Sept. 13, 1944. Div. 4-237-M3 

366. Minimum Capacity Requirements for the BRLG 
Filter Condensers, Willis E. Armstrong, Report 
OD-5-655, NBS, Ordnance Development Division, 
Oct. 10, 1944. Div. 4-237-M4 

167. Revised Amplifier for T-91, Paul E. Landis and 
George Nordquist, Report OD-5-765, NBS, Ord- 
nance Development Division, Mar. 29, 1945. 

Div. 4-238. 225-M7 

168. Change in T-91 Amplifier to Obtain a Longer 
Trimmer Condenser, Cledo Brunetti and George 
Nordquist, Report OD-5-769, NBS, Ordnance De- 
velopment Division, Apr. 2, 1945. Div. 4-237-M8 

169. RF Sensitivity for the Zenith T-172 Unit and 

Variations Thereof, Otto E. Spokas, Report OD- 
7-214R, NBS, Ordnance Development Division, 
Aug. 13, 1945. Div. 4-233-M6 

MEMORANDA OF ORDNANCE DEVELOPMENT 
DIVISION OF NATIONAL BUREAU 
OF STANDARDS 

170. Tests on Reliability of Firing, Minimum Reliable 
Firing Voltage and Time Lags for BS-5 Squibs, 
W. A. Yates, Memorandum PG-319, NBS, Ord- 
nance Development Division, Sept. 30, 1942. 

Div. 4-238.522-MI 

171. Specification Tests on BS-A Squibs, W. A. Yates, 
Memorandum PG-380, NBS, Ordnance Develop- 
ment Division, Nov. 6, 1942. Div. 4-238.521-Ml 

172. Reliability of Firing BS-4 Squibs and Time Tests 
with Radio Frequency Choke and with Resistance 
in Series with Squib, Allen V. Astin and W. A. 
Yates, Memorandum PG-383, NBS, Ordnance De- 
velopment Division, Nov. 9, 1942. 

Div. 4-238.521-M2 


448 


BIBLIOGRAPHY 


173. Test on Minimum Firing Current of BS-U Squib, 
W. A. Yates, Memorandum PG-395, NBS, Ord- 
nance Development Division, Nov. 18, 1942. 

Div. 4-238. 521-M3 

174. Reliability of Firing and Time Test on SA782B, 

Sylvania Thyratrons , W. A. Yates, Memorandum 
PG-412, NBS, Ordnance Development Division, 
Dec. 2, 1942. Div. 4-231.11-MI 

175. Time Lag Specification for BS-4 Squibs, Allen V. 
Astin and W. A. Yates, Service Project OD-27, 
Memorandum Report 29-T, NBS, Ordnance De- 
velopment Division, Jan. 29, 1943. 

Div. 4-238.521-M4 

176. Minimum Voltage to Fire BS-4 Detonators 
through Thyratrons in Complete MC-382 Heads, 
Memorandum from Theodore B. Godfrey to Harry 
M. Diamond, by L. C. Miller, NBS, Ordnance De- 
velopment Division, Dec. 30, 1943. 

Div. 4-238. 521-M7 

177. Firing Circuit Curves, Memorandum from Theo- 

dore B. Godfrey to Messrs. Diamond, Astin, et al., 
NBS, Ordnance Development Division, July 26, 
1944. Div. 4-238. 523-M2 

178. Detonator Firing Test, Memorandum from W. A. 

Yates to Cledo Brunetti, NBS, Ordnance Develop- 
ment Division, Nov. 3, 1944. Div. 4-238.522-M2 

179. Arming Considerations for HVAR, Bertrand J. 
Miller, Memorandum OD-BE-17M, NBS, Ordnance 
Development Division, July 12, 1944. 

Div. 4-244.2-MI 

180. Amplifier with Hum-Bucking for White RGD, 
Philip R. Karr, Memorandum OD-3-28M, NBS, 
Ordnance Development Division, Aug. 8, 1944. 

Div. 4-238.32-M8 

181. Incorporation of RC Arming for T-30, William L. 
Kraushaar, Memorandum OD-3-48M, NBS, Ord- 
nance Development Division, Oct. 20, 1944. 

Div. 4-238. 514-M2 

182. Temperature Coefficient of Condensers Used in the 

10-E Amplifier, F. Jirauch, Memorandum OD-3- 
86M, NBS, Ordnance Development Division, Feb. 
24, 1945. Div. 4-237-M7 

183. Modification of T-30 Amplifier, George Nordquist, 
Memorandum OD-3-88M, NBS, Ordnance Develop- 
ment Division, Mar. 2, 1945. Div. 4-238.225-M4 

184. Possible Uses of Non-Linear Resistors, Philip 
Krupen, Memorandum OD-3-99M, NBS, Ordnance 
Development Division, May 15, 1945. 

Div. 4-236-M12 

185. Revision of Westinghouse T-82, Dorothy R. 

Adams, George Nordquist, and Ralph Stair, Memo- 
randum OD-3-122M, NBS, Ordnance Development 
Division, Aug. 3, 1945. Div. 4-238. 225-M10 

186. Report on Visit to Emerson Company, Memoran- 

dum to W. S. Hinman, Jr., from Philip Krupen, 
NBS, Ordnance Development Division, Apr. 22, 
1943. Div. 4-238.7-MI 

187. Study of Pintell Circuit, Memorandum to W. S. 
Hinman, Jr., from Philip Krupen and F. L. Cooke, 


NBS, Ordnance Development Division, Apr. 30, 
1943. Div. 4-238.7-M2 

188. Request for Laboratory Tests on Performance of 

BS-A Squibs, Memorandum from Cledo Brunetti 
to Theodore B. Godfrey, NBS, Ordnance Develop- 
ment Division, Oct. 18, 1943. Div. 4-238. 521-M5 

189. Relation of Thyratron Repeated Surge Perform- 

ance to Time Delay, Abraham Silverstein, Report 
OD-CT-M8, NBS, Ordnance Development Division, 
Oct. 4, 1944. Div. 4-231.1-M9 

REPORTS OF CONTRACTORS OF DIVISION U 
OF NDRC 

190. Summay'y of Activities in Development and Pilot 

Manufacturing Run of Radio Fuses and Acces- 
sories, Vernon D. Hauck, OEMsr-258, Friez In- 
strument Division, Bendix Aviation Corporation, 
Sept. 27, 1944. Div. 4-100-M4 

191. Preliminary Draft of Final Technical Report 

under Contracts OEMsr-885 and OEMsr-1113, 
Emerson Radio and Phonograph Corporation, May 
14, 1945. Div. 4-100-M6 

192. Final Report of the Federal Telephone and Radio 

Corporation, T. Smith Taylor, OEMsr-941, Fed- 
eral Telephone and Radio Corporation, Oct. 5, 
1943. Div. 4-235-M4 

193. A Radio Proximity Fuze, Type BRTD (Part I), 
OEMsr-949, University of Florida, Sept. 26, 1945. 

Div. 4-211. 21-M13 

194. Generator Powered Radio Proximity Fuze, Type 
T-2005, Muriel E. Pottasch, OEMsr-1437, General 
Instrument Corporation, Aug. 1, 1945. 

Div. 4-222.125-M2 

195. Generator Powered Radio Proximity Fuze for 

Mortars, Longitudinal Excitation Type, Alfred S. 
Khouri, OEMsr-1117, Globe-Union, Inc., Sept. 30, 
1945. ' Div. 4-222. 131-M6 

196. Summay'y Technical Report for Contract OEMsr- 

769, OEMsr-769, State University of Iowa, Sept. 
29, 1945. Div. 4-100-M7 

197. [Alnico Rotor Generators], Final Report oyi Con- 
tract OEMsr-113U, C. W. Clemons, OEMsr-1134, 
Knapp-Monarch Company, Nov. 20, 1944. 

Div. 4-232. 2-M19 

198. [Generators], Final Report on NDRC Conti'act 
OEMsr-981, C. W. Clemons, OEMsr-981, Knapp- 
Monarch Company, Feb. 17, 1944. 

Div. 4-232.2-M11 

199. Final Report (Reserve Battey m y and Low Tempera- 

ture Dry Cells), F. T. Bowditch and A. K. Hunt- 
ley, OEMsr-528, National Carbon Company, Oct. 
26, 1944. Div. 4-232.1-M9 

199a. Final Report of Research and Development 

Conducted by Philco Corporation on P4-772 
Radio Proximity Fuze for Large Bombs, 
R. A. Bell, OEMsr-866, Philco Radio and 
Television Corporation, June 15, 1943. 

Div. 4-211.1-M4 






BIBLIOGRAPHY 


449 


200. Final Progress Report Contract OEMsr-1196, 
Maurice E. Swift, OEMsr-1196, Philco Radio and 
Television Corporation, May 31, 1945. 

Div. 4-211.21-M12 

201. [Vacuum Tubes, Types NR-2 (2B-24), NR-3 

(2C-27) and NR-5 (2E-27)], Final Summary Re- 
port [on] Contract OEMsr-566, A. Abate, OEMsr- 
566, Raytheon Manufacturing Company, Oct. 1, 
1945. Div. 4-231-M5 

202. [Electronic Tubes], Final Report [on] Contract 

OEMsr-630, OEMsr-630, Sylvania Electric Prod- 
ucts, Inc., 1945. Div. 4-231-M4 

203. [Battery Requirements for Project K-4], Final 
Technical Report of Work Performed under 
OEMsr-887, C. B. Pear, Jr., Washington Institute 
of Technology, Feb. 17, 1944. Div. 4-232. 1-M8 

204. Final Technical Report on Generator Powered 

Proximity Fuzes for Bombs, Contract II, K. D. 
Smith and A. L. Stillwell, OEMsr-905, Western 
Electric Company and Bell Telephone Labora- 
tories, May 30, 1944. Div. 4-211. 21-M5 

205. Development of a Ground Approach Proximity 
Fuze for Bomb Nose, BRTG, T. M. Bloomer, 
OEMsr-343 and OEMsr-1106, Termination Report 
CFE-760, Westinghouse Electric and Manufac- 
turing Company, Apr. 28, 1945. Div. 4-211.21-Mll 

206. Proximity Fuze, Bomb, Nose, Ground Approach; 

Type VT, T-32, T. M. Bloomer, OEMsr-343 and 
OEMsr-1106, Termination Report CFE-759, West- 
inghouse Electric and Manufacturing Company, 
Apr. 28, 1945. Div. 4-222.113-M2 

207. RRLG Proximity Fuzes (Final Report), F. H. 
Osborne, OEMsr-1161 and OEMsr-1163, Rudolph 
Wurlitzer Company, Mar. 15, 1945. 

Div. 4-211. 22-MI 

208. Final Technical Report of Work Performed under 

Contract OEMsr-95U, OEMsr-954, Zell Corpora- 
tion, Jan. 12, 1945. Div. 4-100-M5 

209. Mass Production of T-51 Fuzes by the Zenith 

Radio Corporation, Earl J. Diehl, OEMsr-1477, 
Service Project OD-27, Zenith Radio Corporation, 
Oct. 30, 1945. Div. 4-222.112-M5 

210. Generator-Powered Radio Proximity Fuze for 
Mortars: Loop Transverse- Antenna Type, Earl 
J. Diehl, OEMsr-1477, Service Project OD-27, 
Zenith Radio Corporation, Oct. 30, 1945. 

Div. 4-222. 132-MI 

211. Development Report — 1 tV' Diameter Generator 
for Fuze Well, George V. Morris, OEMsr-980, 
Zenith Radio Corporation, Oct. 8, 1943. 

Div. 4-232.2-M7 

UNITED STATES MILITARY PUBLICATIONS 

212. U. S. Army Ordnance Department Tentative Spec- 
ification AXS-1199, February 10, 1944, Detonator, 
Electric, T3. 

213. U. S. Army Signal Corps Specification 371-2088, 
Nov. 19, 1943, Electron Tube 2D29 (Thyratron). 


UNCLASSIFIED TECHNICAL PUBLICATIONS 

214. “An Alternating Current Dynamo with a Flat 
Characteristic for Bicycle Illumination,” H. A. G. 
Hazeu and M. Kiek, Phillips Technical Review, 
Vol. Ill, No. 3, p. 87, March 1938. 

215. Circular C448 of the National Bureau of Stand- 
ards, “Permanent Magnets,” Raymond L. Sanford, 
Aug. 10, 1944. 

216. “Selenium Rectifier Characteristics, Application 
and Design Factors,” C. A. Clarke, Electrical Com- 
munication, Vol. 20, No. 1, 1941. 

217. Radio Engineers Handbook , Frederick E. Ter- 
man, McGraw-Hill Book Co., New York. 

Chapter 4 

REPORTS OF ORDNANCE DEVELOPMENT DIVI- 
SION OF NATIONAL BUREAU OF STANDARDS 

1. Six Speed Regulating Propellers on BRLG Self- 

Reporters (Test Request WBM-9), Aberdeen, De- 
cember 1, 19U3, D. C. Friedman, Report OD-1-76, 
NBS, Ordnance Development Division, Dec. 11, 
1943. Div. 4-232.21-M2 

2. Six Speed Regulating Propellers on Self -Reporters 
(WBM-10) , Aberdeen, January 23, 19 UU, D. C. 
Friedman, Report OD-1-126, NBS, Ordnance De- 
velopment Division, Jan. 31, 1944. 

Div. 4-232.21-M4 

3. Noise Produced by Qear Trains Using Various 

Types of Planetary Gears, P. S. Manov, Report 
OD-4-3, NBS, Ordnance Development Division, 
Oct. 2, 1943. Div. 4-238.512-MI 

4. Speed Regulating Propellers, Jacob Rabinow, Re- 

port OD-4-11, NBS, Ordnance Development Divi- 
sion, Dec. 4, 1943. Div. 4-232.21-MI 

5. Comparison of Generator Rotor Unbalance and 

the Measured Eccentricity, A. Donald Arsem, Re- 
port OD-4-70, NBS, Ordnance Development Divi- 
sion, Dec. 27, 1943. Div. 4-232.22-M3 

6. Report on Mechanical Vibration of the BRLG 

Units Mounted on M-6U Bomb, Jacob Rabinow, 
Report OD-4-32, NBS, Ordnance Development 
Division, Feb. 12, 1944. Div. 4-622-MI 

7. SW-200 Switch Modified to Fire on Contact, Jacob 
Rabinow, Report OD-4-44, NBS, Ordnance De- 
velopment Division, Mar. 31, 1944. 

Div. 4-238.511-M4 

8. Propeller Unbalance Tester, Jacob Rabinow, Re- 

port OD-4-48, NBS, Ordnance Development Divi- 
sion, Apr. 20, 1944. Div. 4-616-MI 

9. Equipment for Balancing Propellers, Jacob Rabi- 

now and A. Donald Arsem, Report OD-4-48 Sup- 
plement, NBS, Ordnance Development Division, 

May 19, 1944. Div. 4-616-M2 

10. Air Travel Required for Release of Arming Cover, 
E. U. Rotor, Report OD-4-54, NBS, Ordnance 
Development Division, Apr. 29, 1944. 

Div. 4-244.1-MI 

Turbine Dynamometer for Determining Input 



450 


BIBLIOGRAPHY 


Torque of Gear Trains, Jacob Rabinow and Louis 
Schuman, Report OD-4-63, NBS, Ordnance De- 
velopment Division, May 10, 1944. Div. 4-612-Ml 

12. Force Required to Pull Out Arming Wire on 

BRLG Unit, Samuel Kolodny, Report OD-4-72, 
NBS, Ordnance Development Division, June 13, 
1944. Div. 4-238.513-Ml 

13. Measurement of Vibration Amplitude of MRLG 
Units, A. Chartock, Report OD-4-73, NBS, Ord- 
nance Development Division, June 14, 1944. 

Div. 4-232. 22-M5 

14. Life Test on Oilite Bearings of MRLG Units, 
A. Chartock, Report OD-4-74, NBS, Ordnance 
Development Division, June 16, 1944. 

Div. 4-232.23-M3 

15. Improvements in the Arming System for the T-50 
Fuze, Jacob Rabinow, Report OD-4-79, NBS, Ord- 
nance Development Division, Aug. 23, 1944. 

Div. 4-238. 513-M2 

16. Effect of Generator End Play on Electrical Noise 

Output, Louis Schuman and A. Donald Arsem, 
Report OD-4-81, NBS, Ordnance Development Di- 
vision, Sept. 7, 1944. Div. 4-232.2-M16 

17. The Use of Precision Bearings in BRLG and T-50 
Noses, Jacob Rabinow, Report OD-4-88, NBS, Ord- 
nance Development Division, Dec. 14, 1944. 

Div. 4-232. 23-M6 

18. Effect of Varying Blade Length and Cover Open- 

ings on Speed Characteristics and Air Thrust on 
Turbine Wheel TFA6070, Louis Schuman, Report 
OD-4-91, NBS, Ordnance Development Division, 
Dec. 29, 1944. Div. 4-232.21-M14 

19. Design of Impact Detonating Element for T-32 
Fuze, Louis Schuman, Report OD-4-96, NBS, Ord- 
nance Development Division, Feb. 17, 1945. 

Div. 4-238. 523-M3 

20. Supporting the T-132 and T-32 Generator to Take 
Setback, Louis Schuman, Report OD-4-101, NBS, 
Ordnance Development Division, Mar. 15, 1945. 

Div. 4-232. 2-M24 

21. Torsion Wire Dynamometer, Louis Schuman, Re- 

port OD-4-105, NBS, Ordnance Development Divi- 
sion, May 26, 1945. Div. 4-612-M2 

22. Proposed Design for Dynamic Balancing Machine, 
Jacob Rabinow, Report OD-4-108, NBS, Ordnance 
Development Division, June 6, 1945. 

Div. 4-616-M8 

23. Method of Assembling Detonators to the T-132 / 

T-171 Interrupter Rotors, Jacob Rabinow, Report 
OD-4-124, NBS, Ordnance Development Division, 
Aug. 3, 1945. Div. 4-238.523-M5 

24. Second Test of Double -Element Setback Pins, 
George T. Parish, Report OD-4-128, NBS, Ord- 
nance Development Division, Sept. 5, 1945. 

Div. 4-238. 513-M4 

25. Nitrided Bearings, Ermo Furlani and Jacob 
Rabinow, Report OD-4-132, NBS, Ordnance De- 
velopment Division, Nov. 6, 1945. 

Div. 4-232. 23-M9 


MEMORANDA OF ORDNANCE DEVELOPMENT 
DIVISION OF BUREAU OF STANDARDS 

26. Setback Switches, Memorandum to Alexander 

Ellett from William B. McLean, Jacob Rabinow, 
and L. M. Andrews, NBS, Ordnance Development 
Division, Mar. 9, 1942. Div. 4-238.511-Ml 

27. Direction of Rotation of Escapement Wheel in 
Setback Arming Devices, Memorandum to Alex- 
ander Ellett from William B. McLean, NBS, Ord- 
nance Development Division, Oct. 10, 1942. 

Div. 4-238.511-M3 

28. Rubber Mounted Generator Rotors, Memorandum 

to Harry M. Diamond from William B. McLean, 
NBS, Ordnance Development Division, Sept. 1, 
1943. Div. 1-232.22-MI 

29. Contact Springs in the BRLG Rotor Housing, 

Memorandum to Harry M. Diamond from William 
B. McLean, NBS, Ordnance Development Division, 
Oct. 8, 1943. Div. 4-232.22-M2 

30. Installation of Oilite Bearings in BRLG Genera- 

tors, Memorandum to Harry M. Diamond from 
William B. McLean, NBS, Ordnance Development 
Division, May 4, 1944. Div. 4-232.23-M2 

31. MRLG Gear Design, Memorandum to William B. 
McLean from Jacob Rabinow, NBS, Ordnance De- 
velopment Division, May 22, 1944. 

Div. 4-238. 515-M3 

32. Calibration of Propeller Unbalance Tester, Memo- 

randum to William B. McLean from A. Donald 
Arsem, NBS, Ordnance Development Division, 
June 30, 1944. Div. 4-616-M3 

33. Measurement of Gam of Balancing Equipment 

(Propeller) , Memorandum to Jacob Rabinow from 
A. Donald Arsem, NBS, Ordnance Development 
Division, July 10, 1944. Div. 4-238.211-M2 

34. Propeller Unbalance Specifications , Memorandum 
to Harry M. Diamond from Jacob Rabinow, NBS, 
Ordnance Development Division, Oct. 16, 1944. 

Div. 4-616-M4 

35. Metal Propeller with Fluted Blades, Memorandum 
to Harry M. Diamond from Jacob Rabinow, NBS, 
Ordnance Development Division, Nov. 1, 1944. 

Div. 4-232. 21-M13 

36. Coupling Shaft in Front Bearing Assemblies, 

Memorandum to Harry M. Diamond from Jacob 
Rabinow, NBS, Ordnance Development Division, 
Nov. 13, 1944. Div. 4-232.23-M5 

37. Visit to New Departure, January 5, 19 U5, Jacob 
Rabinow, Memorandum OD-4-11M, NBS, Ord- 
nance Development Division, Jan. 11, 1945. 

Div. 4-232. 23-M7 

38. Lock Washers, Jacob Rabinow, Memorandum OD- 

4-12M, NBS, Ordnance Development Division, Jan. 
12, 1945. Div. 4-239.2-MI 

39. Some Comments of Field Personnel on Experience 

with Bombs and Fuzes, Jacob Rabinow, Memo- 
randum OD-4-19M, NBS, Ordnance Development 
Division, Jan. 24, 1945. Div. 4-238.515-M4 

40. Eliminating Noise Due to T-50 Gear Trains, Jacob 


BIBLIOGRAPHY 


451 


Rabinow, Memorandum OD-4-21M, NBS, Ord- 
nance Development Division, Feb. 7, 1945. 

Div. 4-238.512-M2 

41. Requirements for Doughnut Mechanism, Jacob 

Rabinow and J. A. Senn, Memorandum OD-4-39M, 
NBS, Ordnance Development Division, Mar. 17, 
1945. Div. 4-238.515-M5 

42. Arming Pin Considerations for the T-132, Jacob 
Rabinow, Memorandum OD-4-44M, NBS, Ord- 
nance Development Division, Apr. 7, 1944. 

Div. 4-238.513-M3 

43. Compilation of Performance of Various Rotors 
Tested for Bursting Speed, Samuel Kolodny, 
Memorandum OD-4-50M, NBS, Ordnance Develop- 
ment Division, Apr. 28, 1945. Div. 4-232. 22-M7 

44. Jolt Test of T-171 Bases, Louis Schuman, Memo- 

randum OD-4-52M, NBS, Ordnance Development 
Division, May 7, 1945. Div. 4-238.3-M4 

45. Clock Rotor for the T-132 1 T-171, Jacob Rabinow, 
Memorandum OD-4-67M, NBS, Ordnance Develop- 
ment Division, June 21, 1945. Div. 4-232. 22-M8 

REPORTS OF CONTRACTORS OF DIVISION 4 
OF NDRC 

46. Development of Balancing Equipment for T-171 

Turbine Assembly, M. S. Redden and Allen S. 
Clarke, OEMsr-1227, Bowen and Company, Elec- 
tronics Division, May 1945. Div. 4-616-M7 

47. Final Technical Report under Contracts OEMsr- 
885 and OEMsr-1113, (Preliminary Draft), 
OEMsr-885 and OEMsr-1113, Emerson Radio and 
Phonograph Corporation, May 14, 1945. 

Div. 4-100-M6 

First Part of Final Report: Interim Reports 31 
through 71, OEMsr-2163, Service Project P4-771R, 
Emerson Radio and Phonograph Corporation. 

48. Summary of Activities in Development and Pilot 
Manufacturing Run of Radio Fuzes and Acces- 
sories and Supplementary Report Covering De- 
velopment of BRLG (Air Driven Alternator Prox- 
imity Fuze), Final Report, Vernon D. Hauck, 
OEMsr-258, Friez Instrument Division, Bendix 
Aviation Corporation, Sept. 27, 1944. 

Div. 4-100-M4 

49. Generator Powered Proximity Fuze, Type T-2005, 
Muriel E. Pottasch, OEMsr-1437, General Instru- 
ment Corporation, Aug. 1, 1945. 

Div. 4-222. 125-M2 

50. Generator Powered Radio Proximity Fuze for 

Mortars, Longitudinal Excitation Type T-132, 
Alfred S. Khouri, OEMsr-1117, Globe-Union, Inc., 
Sept. 30, 1945. Div. 4-222.131-M6 

51. Development and Manufacturing Report on NDRC 
Gear Reduction Unit for VT Bomb Fuze, OEMsr- 
1117, Globe-Union, Inc., Aug. 31, 1945. 

Div. 4-238. 512-M4 

52. [Alnico Rotor Generators], Final Report — Con- 
tract OEMsr-1134, C. W. Clemons, OEMsr-1134, 
Knapp-Monarch Company, Nov. 20, 1944. 

Div. 4-232. 2-M19 


53. Pilot Line Production of BRLG Equipment (Final 

Progress Report), Maurice E. Swift, OEMsr-1196, 
Philco Radio and Television Corporation, May 31, 
1945. Div. 4-211. 21-M12 

54. [The BRLG Unit], Final Report of the OSRD 
Project, Olga E. Yeaton, OEMsr-866, Philco Radio 
and Television Corporation, Aug. 18, 1944. 

Div. 4-211. 21-M6 

55. Research and Development Conducted by Philco 

Corporation on P-4-772 Radio Proximity Fuze for 
Large Bombs, Final Report, R. A. Bell, OEMsr- 
866, Philco Radio and Television Corporation, June 
15, 1943. Div. 4-211. 1-M4 

56. [Development of Special Electronic Devices], Re- 

port to Division 4 y NDRC, on Contract OEMsr- 
1003, Final Report, Alan M. Glover and Arnold R. 
Moore, OEMsr-1003, Radio Corporation of Amer- 
ica, Oct. 23, 1944. Div. 4-231-M3 

57. Final Technical Report of Raymond Engineering 
Laboratory, Inc., on Work Done under Contract 
OEMsr-1378, OEMsr-1378, Report 238, Raymond 
Engineering Laboratory, Inc., Oct. 29, 1945. 

Div. 4-100-M8 

58. [Vacuum Tubes, Types NR-2 (2B-24), NR-3 

(2C-27) and NR-5 (2E-27)]. Final Summary Re- 
port Regarding Development, A. Abate, OEMsr- 
566, Raytheon Manufacturing Company, Oct. 1, 
1945. Div. 4-231-M5 

59. Contracts OEMsr-1161, OEMsr-1163 BRLG Prox- 

imity Fuzes, Final Report, OEMsr-1161 and 
OEMsr-1163, Rudolph Wurlitzer Company, Mar. 
15, 1945. Div. 4-211. 22-MI 

60. Investigation of Rotative Systems of VT-172 and 

V T-132 Units, L. M. K. Boelter, University of 
California, Department of Engineering, October 
1945. Div. 4-232.23-M8 

61. Radio Proximity Fuze, Type MROG, OEMsr-749, 

Part I, Report WRL-UF-4, University of Florida, 
Apr. 2, 1945. Div. 4-211.23-M4 

62. Final Chronological Report on Both the RC Proj- 

ect and the Mortimer Project, Palmer H. Craig, 
OEMsr-749, Report WRL-UF-7, University of 
Florida, May 19, 1945. Div. 4-211. 23-M6 

63. Summary Technical Report for Contract OEMsr- 

769 , OEMsr-769, State University of Iowa, Sept. 
29, 1945. Div. 4-100-M7 

64. Final Technical Report on Generator Powered 
Proximity Fuze for Bombs, Contract II, Western 
Electric Company Bell Telephone Laboratory, 
May 30, 1944. 

65. Photoelectric Fuzes, Final Report, J. F. Wentz, 

OEMsr-145 and OEMsr-225, Bell Telephone Labo- 
ratories, Mar. 1, 1943. Div. 4-212.2-M4 

66. Proximity Fuze, Rocket, Plane-to-Plane, POD 
Type, John R. Boykin, OEMsr-343, Termination 
Report CFE-761, Westinghouse Electric and 
Manufacturing Company, Apr. 28, 1945. 

Div. 4-211.1-M5 

67. Development of a Ground Approach Proximity 
Fuze for Bomb Nose, BRTG, T. M. Bloomer, 


452 


BIBLIOGRAPHY 


OEMsr-343 and OEMsr-1106, Termination Report 
CFE-760, Westinghouse Electric and Manufactur- 
ing Company, Apr. 28, 1945. Div. 4-211.21-M11 

68. Proximity Fuze, Bomb, Nose, Ground Approach: 

Type VT, T-82, T. M. Bloomer, OEMsr-343 and 
OEMsr-1106, Termination Report CFE-759, West- 
inghouse Electric and Manufacturing Company, 
Apr. 28, 1945. Div. 4-222.113-M2 

69. Proximity Fuze, Hornet, John R. Boykin, OEMsr- 

343, Termination Report CFE-762, Westinghouse 
Electric and Manufacturing Company, Apr. 28, 
1945. Div. 4-211. 1-M6 

70. Final Technical Report of Work Performed under 

Contract OEMsr-95U, OEMsr-954, Zell Corpora- 
tion, Jan. 12, 1945. Div. 4-100-M5 

71. Generator Powered Radio Proximity Fuze for 

Bombs Transverse Antenna Type, Final Report, 
Earl J. Diehl, OEMsr-980 and OEMsr-1133, Serv- 
ice Project OD-27, Zenith Radio Corporation, Mar. 
30, 1945. Div. 4-211.21-M9 

72. Generator Powered Radio Proximity Fuze for 
Mortars: Loop Transverse Antenna Type, Earl J. 
Diehl, OEMsr-1477, Service Project OD-27, Zenith 
Radio Corporation, Oct. 30, 1945. 

Div. 4-222. 132-MI 

73. Development and Manufacturing Report on NDRC 
Gear Reduction Unit for VT Rocket Fuze, OEMsr- 
1117, Globe-Union, Inc., Sept. 14, 1945. 

Div. 4-238.512-M4 

74. RRLG Proximity Fuzes, Final Report, F. H. Os- 
borne, OEMsr-1161 and OEMsr-1163, Rudolph 
Wurlitzer Company, Mar. 15, 1945. 

Div. 4-211. 22-MI 

75. Pilot Production of T-50 Fuzes, Allen S. Clarke 
and C. N. Julian, OSRD 5351, OEMsr-1227, Serv- 
ice Projects OD-27, NO-77B, and NO-77R, Report 
A-335, Bowen and Company, Apr. 12, 1945. 

Div. 4-222. 111-M3 

76. Generator-Powered Proximity Fuzes for Bombs 

(Final Technical Report), K. D. Smith and A. L. 
Stillwell, OEMsr-905, Bell Telephone Laboratories, 
Mar. 24, 1944. Div. 4-211.21-M5 

77. [Battery Requirements for Project K-4], Final 
Technical Report on Work Performed on Contract 
OEMsr-887, C. B. Pear, Jr., OEMsr-887, Wash- 
ington Institute of Technology, Feb. 17, 1944. 

Div. 4-232.1-M8 

78. Generator-Powered Radio Proximity Fuze, Type 
T-2005, Muriel E. Pottasch, OEMsr-1437, General 
Instrument Corporation, Aug. 1, 1945. 

Div. 4-222. 125-M2 


Chapter 5 

1. Radio Proximity Fuze for Plane-to-Plane Rocket 
Application, Harry M. Diamond, W. S. Hinman, 
Jr., Robert D. Huntoon, Cledo Brunetti, and C. N. 
Page, Service Projects OD-27 and OD-26, Report 


A-144, Armor and Ordnance of NDRC, Feb. 12, 
1943. Div. 4-211.1-M3 

2. The Air Burst Proximity Fuze for Bombs, Rockets, 
and Mortars, NBS, Ordnance Development Divi- 
sion, National Bureau of Standards, October 1945. 

Div. 4-211-M3 

3. Computation of Burst Heights of Longitudinally - 

Excited Bomb Fuzes, R. P. Schwartz, Report OD- 
3-281, NBS, Ordnance Development Division, Aug. 
7, 1945. Div. 4-241-M8 

4. “VT Rocket Fuzes (for Aircraft Rockets),” Ord- 
nance Pamphlet 1470, Apr. 6, 1945. 

5. Fuze, Rocket, PD, T-6, TB 9X-93, Dec. 19, 1944. 

6. Fuze, Rocket, P.D., T-4 and T-5, TB 9X-94, Dec. 
28, 1944. 

7. VT Bomb Nose Fuzes, TB 9X-106, Feb. 21, 1945. 

8. Test of Fuze, Bomb, Nose T51E1, Army Air 
Forces (Eglin Field) S.T.P. 1-45-6, Nov. 27, 1945. 

SPECIFICATIONS FOR METAL PARTS 
ASSEMBLIES OF FUZES 

9. Specifications for the Manufacture and Testing of 
the M-3 (MC-382) Radio Fuze, Cledo Brunetti, 
NDRC, Division 4, Sept. 30, 1942. 

Div. 4-222. 128-MI 

10. Technical Specifications for Parts Assemblies for 

VT Reaction Grid Detection Fuzes, T-30 and 
T-200U, Draft 2, NBS, Ordnance Development 
Division, July 20, 1945.* Div. 4-222.126-M2 

11. Specification for Longitudinally Excited, Genera- 
tor Powered Radio Proximity Fuze, BRLG-100, 
NDRC, Division 4, Feb. 25, 1944. 

Div. 4-211.21-M4 

12. Fuze, Bomb, Nose, VT, M-168, Parts Assembly, 
Tentative Specification, Ordnance Department, 
U. S. Army, AXS-1691, Apr. 18, 1946. 

13. Specification for Transversely Excited, Generator 

Powered Radio Proximity Fuze, T-51E1, NDRC, 
Division 4, Jan. 5, 1945. Div. 4-211. 21-M8 

14. Fuze, Bomb, Nose, VT, T-82E2, Parts Assembly, 
Tentative Specification, Ordnance Department, 
U. S. Army, AXS-1610, July 19, 1945. 

15. Fuze, VT, T-132, Parts Assembly, Tentative Speci- 
fication, Ordnance Department, U. S. Army, AXS- 
1615, July 1, 1945. 

16. Fuze, VT, T-171, Parts Assembly, Tentative Speci- 
fication, Ordnance Department, U. S. Army, AXS- 
1667, July 23, 1945. 

Chapter 6 

ARMOR AND ORDNANCE REPORTS OF NDRC 

1. Generator-Powered Radio Proximity Fuze for 
Bombs Transverse Antqypia Type, Earl J. Diehl, 
OSRD 5111, OEMsr-980 and OEMsr-1133, Service 

* No official specification was published for the OD 
models. The specifications for the OD and RGD models 
are quite similar except for the RF loading procedure 
and except for the audio input test circuit. 


BIBLIOGRAPHY 


453 


Projects OD-27 and NO-77B, Final Report A-326, 
Zenith Radio Corporation, Mar. 30, 1945. 

Div. 4-211.21-M10 

2. Pilot Production of T-50 Fuzes, Allen S. Clarke 
and C. N. Julian, OSRD 5351, OEMsr-1227, Serv- 
ice Projects OD-27, NO-77B, and NO-77R, Report 
A-335, Bowen and Company, Apr. 12, 1945. 

Div. 4-222.111-M3 

REPORTS OF ORDNANCE DEVELOPMENT DIVI- 
SION OF NATIONAL BUREAU OF STANDARDS 

3. Engineering Letters Nos. 1 to 63, Inclusive, Cover- 

ing tine Period May 27, 19 UU to August 29, 1945 
(No. 58 not microfilmed), NBS, Ordnance De- 
velopment Division. Div. 4-100-M3 

(The aforementioned Engineering Letters cover 
a variety of items relating to production problems 
for radio proximity fuzes. They were prepared by 
the Production Engineering Section of the Ord- 
nance Development Division and transmitted to 
the various manufacturers engaged in production 
of fuzes.) 

REPORTS OF CONTRACTORS OF DIVISION U 
OF NDRC 

4. Summary of Activities in Development and Pilot 

Manufacturing Run of Radio Fuzes and Acces- 
sories, Vernon D. Hauck, OEMsr-258, Friez In- 
strument Division, Bendix Aviation Corporation, 
Sept. 27, 1944. Div. 4-100-M4 

5. Preliminary Draft of Final Technical Report 
under Contracts OEMsr-885 and OEMsr-1113, 
OEMsr-885 and OEMsr-1113, Emerson Radio and 
Phonograph Corporation, May 14, 1945. 

Div. 4-100-M6 

6. [Development of the 7-mm Rectifier Disc], Final 

Report of the Federal Telephone and Radio Cor- 
poration, T. Smith Taylor, OEMsr-941, Oct. 5, 
1943. Div. 4-235-M4 

7. Generator-Powered Radio Proximity Fuze, Type 
T-2005, Muriel E. Pottasch, OEMsr-1437, General 
Instrument Corporation, Aug. 1, 1945. 

Div. 4-222. 125-M2 

8. Generator-Powered Radio Proximity Fuze for 

Mortars, Longitudinal Excitation Type, T-132, 
Alfred S. Khouri, OEMsr-1117, Globe-Union, Inc., 
Sept. 30, 1945. Div. 4-222.131-M6 

9. [Alnico Rotor Generators], Final Report, Con- 
tract OEMsr-1134, C. W. Clemons, OEMsr-1134, 
Knapp-Monarch Company, Nov. 20, 1944. 

Div. 4-232. 2-M19 

10. [Generators], Final Report on Contract OEMsr- 

981, C. W. Clemons, OEMsr-981, Knapp-Monarch 
Company, Feb. 17, 1944. Div. 4-232.2-M11 

11. Final Progress Report, Contract OEMsr-1196, 

Maurice E. Swift, OEMsr-1196, Philco Corpora- 
tion, May 31, 1945. Div. 4-211.21-M12 

12. Final Technical Report on Generator-Powered 


Proximity Fuzes for Bombs, K. D. Smith and A. L. 
Stillwell, OEMsr-905, Contract II, Western Elec- 
tric Company, Bell Telephone Laboratories, May 
30, 1944. Div. 4-211.21-M5 

13. Development of a Ground Approach Proximity 
Fuze for Bomb, Nose, BRTG, T. M. Bloomer, 
OEMsr-343 and OEMsr-1106, Termination Report 
CFE-760, Westinghouse Electric and Manufac- 
turing Company, Apr. 28, 1945. 

Div. 4-211. 21-M11 

14. Proximity Fuze, Bomb, Nose, Ground Approach, 

Type VT, T-82, T. M. Bloomer, OEMsr-343 and 
OEMsr-1106, Termination Report CFE-757, West- 
inghouse Electric and Manufacturing Company, 
Apr. 28, 1945. Div. 4-222.113-M2 

15. Final Technical Report of Work Performed under 

Contract OEMsr-954, OEMsr-954, Zell Corpora- 
tion, Jan. 12, 1945. Div. 4-100-M5 

16. Generator-Powered Radio Proximity Fuze for 
Mortars, Loop Transverse-Antenna Type, Earl J. 
Diehl, OEMsr-1477, Service Project OD-27, Zenith 
Radio Corporation, Oct. 30, 1945. 

Div. 4-222. 132-MI 

17. Mass Production of T-51 Fuzes by Zenith Radio 
Corporation (OEMsr-980 and OEMsr-1133), Oct. 
3, 1945. 


Chapter 7 

ARMOR AND ORDNANCE REPORTS OF NDRC 

1. Analysis of Feedback Amplifiers for MC-382 

Fuzes. Robert D. Huntoon, William L. Kraushaar, 
and Herbert D. Cook, Progress Report A122, Dec. 
7, 1942. Div. 4-238. 222-MI 

2. Pilot Production of T-50 Fuzes, Allen S. Clarke 
and C. N. Julian, OSRD 5351, OEMsr-1227, Serv- 
ice Projects OD-27, NO-77B and NO-77R, Report 
A-335, Bowen and Company, Apr. 12, 1945. 

Div. 4-222. 111-M3 

NDRC REPORTS AND MEMORANDA 

3. Radiation Properties of BRLG, Robert D. Hun- 

toon, Service Project OD-27, Memorandum Report 
43-R, July 29, 1942. Div. 4-243.11-MI 

4. Description of 1000-G Centrifuge, Allen S. Clarke, 
Eng. Memorandum, Nov. 25, 1942. Div. 4-615-MI 

5. Engineering Report on MC-382 Test Equipment, 
Preliminary Draft, Nov. 26, 1942. 

Div. 4-222.128-M3 

NDRS SPECIFICATIONS 

6. Specification for Electron Tube NR-2A, a Diode 

Tube, Aug. 1, 1944. Div. 4-231.2-M3 

7. ' Specification for Generator G-l, NBS, Ordnance 

Development Division, Nov. 25, 1944. 

Div. 4-232.2-M20 


454 


BIBLIOGRAPHY 


REPORTS OF ORDNANCE DEVELOPMENT DIVI- 
SION OF NATIONAL BUREAU OF STANDARDS 

8. Electronic Frequency Meter , Charles Ravitsky, 
Leonard C. Pochop, and J. G. Reid, Jr., Report 0D- 

2- 15 (First Series), NBS, Ordnance Development 

Division, July 26, 1943. Div. 4-613-MI 

9. Rotary Shaker for Pre-Testing BRLG Heads , 
Robert D. Huntoon, Report OD-3-7, NBS, Ord- 
nance Development Division, Oct. 22, 1943. 

Div. 4-614-MI 

10. Critical Grid Voltage of Thyratrons and Hum 

Voltage Output of BRLG-11, F. Lamar Cooke, 
Report OD-3-9, NBS, Ordnance Development Divi- 
sion, Oct. 27, 1943. Div. 4-231.1-M7 

11. Methods of Measuring the Critical Voltage of 

Thyratrons, F. Lamar Cooke, Report OD-3-13, 
NBS, Ordnance Development Division, Oct. 28, 
1943. Revised: Nov. 9, 1943. Div. 4-231. 1-M8 

12. Generator Performance, William L. Kraushaar, 

Report OD-3-17, NBS, Ordnance Development Di- 
vision, Nov. 1, 1943. Div. 4-232.2-M8 

13. Preliminary Report on Tuning and Loading Device 
for BRLG, Paul E. Landis, Report OD-3-37, NBS, 
Ordnance Development Division, Nov. 29, 1943. 

Div. 4-233. 1-MI 

14. Tuning BRLG, Robert D. Huntoon, Report OD- 

3- 87, NBS, Ordnance Development Division, Jan. 

29, 1944. Div. 4-233.1-M2 

15. BRLG Tuning on Various Vehicles, Bertrand J. 

Miller, Report OD-3-106 and Addendum OD-3- 
106A, Mar. 3 and 20, 1944. Div. 4-231.2-M2 

16. Addendum to Report OD-3-106, Bertrand J. Miller 
and Charles C. Gordon, Report OD-3-106A, NBS, 
Ordnance Development Division, Mar. 20, 1944. 

Div. 4-231.2-M2 

17. Microphonic Stability of Oscillator-Diode Type 

Fuze Circuits, Robert D. Huntoon, Report OD-3- 
117, NBS, Ordnance Development Division, Mar. 
22, 1944. Div. 4-238.31-MI 

18. Loading Circuit for Final Test Chamber to Be 
Used at W Frequency ayid Encasing Cup Speci- 
fication, Thomas C. Bagg, Report OD-3-126, NBS, 
Ordnance Development Division, Apr. 1, 1944. 

Div. 4-233.1-M3 

19. Testing RGD Units, Philip Krupen, Report OD- 

3-131, NBS, Ordnance Development Division, Apr. 
22, 1944. Div. 4-238.32-M6 

20. Dummy Antennas, Robert D. Huntoon, Report OD- 

3-133, NBS, Ordnance Development Division, Apr, 
29, 1944. Div. 4-233-M3 

21. Preliminary Investigation of Characteristics of 

Test Chamber, with Respect to Relative Position 
of Unit Therein, J. L. Pike and Otto E. Spokas, 
Report OD-3-135, NBS, Ordnance Development 
Division, Apr. 25, 1944. Div. 4-233. 1-M4 

22. Electronic Tachometer, Herbert D. Cook, Report 

OD-3-137, NBS, Ordnance Development Division, 
July 28, 1944. Div. 4-621.1-MI 


23. Triode Microphonics, Robert D. Huntoon, Report 

OD-3-153, NBS, Ordnance Development Division, 
May 20, 1944. Div. 4-231.3-M2 

24. Compensated Resistors for Tuning and Loading 

Standards, E. Eisner and Paul T. Hawes, Report 
OD-3-154, NBS, Ordnance Development Division, 
May 24, 1944. Div. 4-236-M4 

25. Resonant Loading of BRTG Units by Test Boxes, 
Ralph Stair, Glenn L. Scillian, and Leonard C. 
Pochop, Report OD-3-196, NBS, Ordnance De- 
velopment Division, Nov. 13, 1944. 

Div. 4-233.1-M7 

26. The T-132 (Mortar Fuze) Apex Performance 

Problem, William L. Kraushaar, Report OD-3-220, 
NBS, Ordnance Development Division, Mar. 3, 
1945. Div. 4-222. 131-M2 

27. Test Fixture for Balancing the Single Bearing 

Nose Assembly, Jacob Rabinow, Supplement 3 to 
Report OD-4-48, NBS, Ordnance Development 
Division, Jan. 13, 1945. Div. 4-616-M6 

28. Compression Test Equipment, C. Chartock, Report 

OD-4-50, NBS, Ordnance Development Division, 
Apr. 27, 1944. Div. 4-623-MI 

29. Torsion Wire Dynamometer, Louis Schuman, Re- 

port OD-4-105, NBS, Ordnance Development Divi- 
sion, May 26, 1945. Div. 4-612-M2 

30. Proposed Design for Dynamic Balancing Machine, 
Jacob Rabinow, Report OD-4-108, NBS, Ordnance 
Development Division, June 6, 1945. 

Div. 4-616-M8 

31. Report of Shelf Life Test on MC-382 Unit, Paul J. 
Martin, Report OD-5-522, NBS, Ordnance De- 
velopment Division, Oct. 12, 1944. 

Div. 4-238.222-M5 

32. A Study of the Development of the BRLG-100 

Specifications of February 25, 19 UU, Report OD- 
5-617, NBS, Ordnance Development Division, Sept. 
1, 1944. Div. 4-211.21-M7 

33. A Study of the Development of the Specification 

for the Rectifier Bridge Assembly RA-1 of July 
5, 19 Uh, Report OD-5-637, NBS, Ordnance Develop- 
ment Division, Oct. 4, 1944. Div. 4-235-M2 

34. A Study of the Development of the NDRC Speci- 
fication for Generator G-l Dated February 25, 
19 UU, Report OD-5-645, NBS, Ordnance Develop- 
ment Division, Oct. 6, 1944. Div. 4-232. 2-M 17 

35. A Study of the Development of the Specifications 

for NR-2A Diode, NR-3 /NS-3 Triode, NS-A Thy- 
ratron and NR-5 / NS-5 Pentode, Dated August 1, 
19 H, Report OD-5-671, NBS, Ordnance Develop- 
ment Division, Oct. 20, 1944. Div. 4-231-M2 

36. Zenith Revised Final Test Position, Paul E. 

Landis, Report OD-5-787, NBS, Ordnance Develop- 
ment Division, Apr. 16, 1945. Div. 4-622-M3 

37. Mechanical Properties of Final Test Chamber, 

Robert D. Huntoon and T. F. Protz, Report OD- 
BE-9R, NBS, Ordnance Development Division, 
July 24, 1944. Div. 4-619-M2 

38. A New Proposal for Shaking Each Unit in Final 


CHET 


BIBLIOGRAPHY 


455 


Test, Wendell L. Lees, Report OD-BEr72R, NBS, 
Ordnance Development Division, Feb. 24, 1945. 

Div. 4-622-M2 

39. Compensated Tuning Resistors Used in Tuning 

T-30 Fuzes for Aircraft Rockets (AR and HVAR), 
Paul T. Hawes and Thomas C. Bagg, Report OD- 
TEG-6R, NBS, Ordnance Development Division, 
Dec. 14, 1944. Div. 4-236-M7 

40. Test Line for T-132 Unit, Globe-Union and Wur- 

litzer Model, Thomas C. Bagg, Engineering Report 
OD-2-TEG-SR, NBS, Ordnance Development Di- 
vision, Jan. 30, 1945. Div. 4-222.131-MI 

41. Measurement of Firing Voltage, Robert D. Hun- 

toon, Project OD-3, NBS, Ordnance Development 
Division, Aug. 20, 1943. Div. 4-621-M2 

42. Electronic Demagnetizer, Engineering Letter 40, 
Jan. 3, 1945. 

MEMORANDA OF ORDNANCE DEVELOPMENT 
DIVISION OF NATIONAL BUREAU 
OF STANDARDS 

43. Loading Device for BRTG Units, L. A. Riley and 
G. J. Tedore, Memorandum OD-5-88M, NBS, Ord- 
nance Development Division, Dec. 26, 1944. 

Div. 4-233.1-M8 

44. Compensated Versus Uncompensated Resistors 
for Sensitivity Measurements on RGD Units, Paul 
E. Landis, Memorandum OD-5-242M, NBS, Ord- 
nance Development Division, June 25, 1945. 

Div. 4-328.2-M2 

45. Noise Differences in Final Test Chambers, Robert 
D. Huntoon, Memorandum OD-BE-11M, NBS, 
Ordnance Development Division, June 26, 1944. 

Div. 4-233.1-M6 

46. Blocking Voltage for Use in Making Audio Test 

on OD Units, Herbert D. Cook, Memorandum OD- 
TEG-35M, NBS, Ordnance Development Division, 
Feb. 12, 1945. Div. 4-621-M4 

47. Hum Injection Adjustment, Charles R. Duke, 

Herbert D. Cook, and Thomas C. Bagg, Memo- 
randum OD-TEG-78M, NBS, Ordnance Develop- 
ment Division, July 28, 1945. Div. 4-621-M5 

48. Tuning and Adjustment of MC-382. Memorandum 
to Harry Diamond from W. S. Hinman, Jr., NBS, 
Ordnance Development Division, Nov. 16, 1942. 

Div. 4-222.128-M2 

REPORTS OF CONTRACTORS OF 
DIVISION U NDRC 

49. Radiation Dummy Load Consideration, MC-382, 

R. H. Pintell, Service Project OD-27, Memorandum 

Report 33R, Emerson Radio and Phonograph Cor- 
poration, Mar. 2, 1943. Div. 4-243.12-MI 

50. Development of Balancing Equipment for T-171 
Turbine Rotor Assemblies, M. S. Redden and Allen 

S. Clarke, OEMsr-1227, Bowen and Company, 

May 1945. Div. 4-616-M7 

51. Mass Production of T-51 Fuzes by Zenith Radio 


Corporation, Earl J. Diehl, OEMsr-1477, Service 
Project OD-27, Zenith Report of Contract W-28- 
004-SC-965, Oct. 30, 1945. Div. 4-222.112-M5 

U. S. MILITARY REPORTS 

52. Tentative Specifications for Rectifiers, AXS-1613, 
Mar. 31, 1945. 

53. Tentative Specifications for Tubes, Vacuum, and 
Gas Filled. Ordnance Department, U. S. Army, 
AXS-1612 (Revision 1), July 25, 1945. 

54. War Department Technical Manual for Quality 
Control Testing for Ring-Type and Bar-Type VT 
Nose Metal Parts Assemblies for Bombs and 
Rockets. 

UNCLASSIFIED TECHNICAL PUBLICATIONS 

55. Measurements of Admittance at UHF. J. M. Miller 
and B. Salzberg, RCA Review 3, April 39, p. 486. 


DRAWING REFERENCES 


Drawing Reference 
N umber 
1 
2 

3 

4 

5 

6 

7 

8 
9 


NBS Drawing Index 
L5515 
L5516 
L5524 
L5526 
L5529 
L5530 
L5531 
L5532 
L5533 


Chapter 8 

ARMOR AND ORDNANCE REPORTS AND 
MEMORANDA OF NDRC 

1. Radio Reporters for Proximity Fuze Testing, 

Allen V. Astin, OSRD 589, Report A-53, May 21, 
1942. Div. 4-611-MI 

2. Proving Ground Operations and Facilities for 

Testing Proximity Fuzes for Bombs and Rockets, 
Lauriston S. Taylor, OSRD 719, Memorandum 
A-44M, July 20, 1942. Div. 4-222.129-MI 

3. Note on a Practical Method for the Field Testing 
of Radio Proximity Fuzes for Rocket Applications, 
Harry M. Diamond and W. S. Hinman, Jr., OSRD 
767, Memorandum A-48M, July 30, 1942. 

Div. 4-222. 129-M2 

4. Sampling Formulas for Qualification and Proof 
Testing of Production Lots, T. M. White, OSRD 
3198, Memorandum A-82M, January 1944. 

Div. 4-770-MI 

NDRC ENGINEERING REPORTS 

5. Proposed Proof Range for M-2 and M-3 Fuzes at 
Aberdeen, Harry M. Diamond, Service Project 
OD-27, Memorandum Report 1-M, Dec. 29, 1942. 

Div. 4-222. 223-MI 


456 


BIBLIOGRAPHY 


6. Chapter 4 (“Exterior Ballistics”) of Rocket Fun- 

damentals ; prepared under the auspices of Section 
H, Division 3, edited by Bryce L. Crawford, Jr., 
OSRD 3992, OEMsr-273, Report ABL-SR4, George 
Washington University, 1944. Div. 4-410-MI 

7. Chapter 13 (“Flight Tests of Rockets”) of Rocket 

Fundamentals, prepared under the auspices of 
Section H, Division 3 (OSRD 3992), Report ABL- 
SR4, 1944. Div. 4-410-MI 

REPORTS AND MEMORANDA OF ORDNANCE 
DEVELOPMENT DIVISION OF NATIONAL 
BUREAU OF STANDARDS 

8. Frequency of Yaw of Budd UVz" Rockets Fired 
from a Plane, Theodore B. Godfrey, Service Proj- 
ect OD-27, Memorandum Report 47-T, NBS, Ord- 
nance Development Division, Feb. 11, 1943. 

Div. 4-412.2-MI 

9. Three-Dimensional Analysis of 11 Trajectories of 
PEP-M2 Fuzes Fired from a Plane at Aberdeen, 
January 23 and 2U, 19 U3, Theodore B. Godfrey, 
Service Project OD-27, Memorandum Report 54-T, 
NBS, Ordnance Development Division, Feb. 11, 

1943. Div. 4-222-224-M5 

10. Yaw Reporter Test, Theodore B. Godfrey and 

L. C. Miller, Service Project OD-27, Memorandum 
Report 401-T, NBS, Ordnance Development Divi- 
sion, Aug. 9, 1943. Div. 4-412.2-M2 

11. Salvo Firing in Search of Sympathetic Function- 
ing of MC-380 and MC-382 Fuzes, F. R. Kotter 
and T. N. White, Report OD-1-15, NBS, Ordnance 
Development Division, Sept. 23, 1943. 

Div. 4-245-MI 

12. Puff Delay, 500-lb Bomb, Theodore B. Godfrey, 

Report OD-1-41, NBS, Ordnance Development 
Division, Nov. 5, 1943. Div. 4-242.13-MI 

13. A Modified Method of Scanning Phonograms, J. J. 
Hopfield, Report OD-1-130, NBS, Ordnance De- 
velopment Division, Feb. 5, 1944. Div. 4-617-MI 

14. Field Test of SW200 0.7-Sec Switches; Photo- 
graphic Method for Timing Early Functions in 
High Angle Firing, H. F. Stimson, R. G. Tobey, 
and D. W. Scott, Report OD-1-237, NBS, Ordnance 
Development Division, Apr. 20, 1944. 

Div. 4-238. 511-M5 

15. Static Tests of BRLG Function Indicators, T. C. 

Hellmers, L. L. Parker, and L. C. Miller, Report 
OD-1-272, NBS, Ordnance Development Division, 
May 3, 1944. Div. 4-626-MI 

16. UO Bowen T-50 E10 on Refrigerated Mk 7, D. A. 
Worcester and D. W. Scott, Report OD-1-529, 
NBS, Ordnance Development Division, Oct. 20, 

1944. Div. 4-222. 127-MI 

17. Field Test, Rotation of M9A1 with Hand-Crimped 

Fins, R. G. Tobey and D. W. Scott, Report OD- 
1-588, NBS, Ordnance Development Division, Dec. 
18, 1944. Div. 4-412.2-M3 

18. Static Tests to Determine the Effect of Different 
Trap and Motor Combinations on the Functioning 


of the T-5 Fuze, H. F. Stimson, John Beek, Jr., 
E. Allen Cook, and Charles C. Gordon, Report 
OD-1-589, NBS, Ordnance Development Division, 
Dec. 15, 1944. Div. 4-222.121-M7 

19. Ballistics of Mk 1 and Mk 7 Motors with T-50 

and T-51 Units and Slip Factor Data for Various 
Vehicles, D. C. Friedman and G. L. Rabinow, Re- 
port OD-1-591, NBS, Ordnance Development Divi- 
sion, Dec. 21, 1944. Div. 4-411. 1-M5 

20. Plane Firing of T-30 and Mk 7, D. W. Scott, Re- 

port OD-1-650, NBS, Ordnance Development Divi- 
sion, Feb. 7, 1945. Div. 4-222.124-MI 

21. Effect of Rocket Spin upon the Performance of 
VT Fuzes T-U, T-5, T-6, Theodore B. Godfrey, 
Summary Report OD-1-668, NBS, Ordnance De- 
velopment Division, Mar. 13, 1945. 

Div. 4-222. 123-M3 

22. Plane Firing, Philco T-200U on T-87 , D. A. Wor- 
cester and D. W. Scott, Report OD-1-744, NBS, 
Ordnance Development Division, May 10, 1945. 

Div. 4-222. 125-Ml 

23. Visibility of Various Mortar Spotting Charges, 

R. G. Tobey and G. Rabinow, Report OD-1-829, 
NBS, Ordnance Development Division, July 11, 

1945. Div. 4-626-M2 

24. Afterburning from Rocket Motors and Malfunc- 

tioning of VT Fuzes, H. F. Stimson, Report OD- 
1-896, NBS, Ordnance Development Division, Oct. 
15, 1945. Div. 4-411. 11-M6 

25. An Investigation of Mo7'tar-Shell Muzzle Veloc- 
ities, H. V. Menapace, M. H. Seibel, and G. L. 
Rabinow, Report OD-1-909, NBS, Ordnance De- 
velopment Division, Mar. 14, 1946. Div. 4-515-MI 

26. A Method of Recording Size and Concentration of 
Raindrops, Theodore B. Godfrey, R. K. Pickels, 
and D. A. Worcester, Report OD-1-920, NBS, Ord- 
nance Development Division, May 21, 1946. 

Div. 4-740-MI 

27. Equivalent Release Co7iditio7is for Level Flight 

Bombmg and Dive Bombing, Irene Freuder, F. L. 
Celauro, and T. N. White, Technical Memorandum 
OD-1-TM2, NBS, Ordnance Development Divi- 
sion, Oct. 30, 1945. Div. 4-211. 3-M5 

28. Audio Limiter, W. A. Yates, Technical Memoran- 

dum OD-1-TM5, NBS, Ordnance Development Di- 
vision, Oct. 29, 1945. Div. 4-617-M2 

29. Recording Oscilloscope and 16-mm Eastman 
Oscilloscope Camera, N. Newman, Technical 
Memorandum OD-1-TM8, NBS, Ordnance De- 
velopment Division, Nov. 2, 1945. 

Div. 4-617-M3 

30. Intermittent Reco7'ding Control, N. Newman, 
Technical Memorandum OD-1-TM9, NBS, Ord- 
nance Development Division, Nov. 7, 1945. 

Div. 4-617-M4 

31. Fifty-Cycle Oscillator, N. Newman, Technical 
Memorandum OD-1-TM10, NBS, Ordnance De- 
velopment Division, Nov. 7, 1945. Div. 4-619-M5 

32. Notes on Loading, Assembly a7id Storage Pro- 



BIBLIOGRAPHY 


457 


cedures in Rocket Testing at Blossom Point Prov- 
ing Ground, R. G. Robey and L. T. Johnson, Tech- 
nical Memorandum OD-1-TM19, NBS, Ordnance 
Development Division, Sept. 25, 1945. 

Div. 4-412.4-M7 

33. Notes on Mock-Plane Target, Rocket Launchers 
and Firing Procedures at Blossom Point, A. P. 
Sutten, Technical Memorandum OD-1-TM20, NBS, 
Ordnance Development Division, Sept. 25, 1945. 

Div. 4-412. 4-M8 

34. Notes on Drainage, Firing Tower Construction, 
Fire Prevention and Observational Procedures at 
Blossom Point Proving Ground, R. G. Tobey, Tech- 
nical Memorandum OD-1-TM21, NBS, Ordnance 
Development Division Sept. 25, 1945. 

Div. 4-412.4-M9 

35. Navy Rocket Trajectory Analysis, A. L. Leiner, 

Memorandum OD-2-203, NBS, Ordnance Develop- 
ment Division, May 5, 1945. Div. 4-412.1-M8 

36. Standard Statistical Methods for Testing the 
Difference between Mean Values, B. M. Bennett, 
Memorandum OD-2-205M, NBS, Ordnance De- 
velopment Division, May 7, 1945. Div. 4-770-M3 

37. Early Functions of MC-382 Radio-operated Plane- 

to-Plane Rocket Fuze, Bertrand J. Miller and 
Robert D. Huntoon, Progress Report OD-3-AB2, 
NBS, Ordnance Development Division, June 8, 
1943. Div. 4-222. 128-M12 

38. Tests BJM-5 and BJM-6, Charles Ravitsky, Prog- 
ress Report OD-7-206R, NBS, Ordnance Develop- 
ment Division, May 14, 1945. Div. 4-222. 124-M3 

39. Sequential Analysis of Statistical Data: Applica- 

tions, T. N. White and H. C. Doob, Report OD- 
OAG-46, NBS, Ordnance Development Division, 
Sept. 27, 1944. Div. 4-770-M2 

40. [Cenco Rocket] Motor, NBS Drawing 440 R, NBS, 
Ordnance Development Division, May 20, 1942. 

Div. 4-411.1-M2 

REPORTS OF CONTRACTORS OF DIVISION U 
OF NDRC 

41. Chapter VI of Summary Technical Report, Con- 
tract OEMsr-769, submitted by James A. Jacobs, 
State University of Iowa, Sept. 29, 1945. 

Div. 4-100-M7 

42. Chapter VII of Summary Technical Report, Con- 
tract OEMsr-769, submitted by James A. Jacobs, 
State University of Iowa, Sept. 29, 1945. 

Div. 4-100-M7 

43. Clinton Field Station Report 60, State University 
of Iowa. 

44. Mortar Fuze Recovery, W. E. Nickell OEMsr-769, 

Report MB-3-1-45, State University of Iowa, Mar. 
31, 1945. Div. 4-619-M4 

45. The Calculation of Trajectories, L. E. Ward, 
OEMsr-769, Technical Report T3-8-1-45, State 
University of Iowa, Aug. 29, 1945. Div. 4-512-M3 

46. The Effects on Trajectories of Small Changes in 
Initial Conditions with Aioplication to Wind Cor- 


rections, L. E. Ward, OEMsr-769, Technical Re- 
port T3-9-1-45, State University of Iowa, Sept. 12, 
1945. Div. 4-512-M4 

UNITED STATES MILITARY PUBLICATIONS 

47. War Department Manual TM11-2U10. 

48. Handbook of Instructions and Parts Catalog 
AN 10-25-50. 


Chapter 9 

ARMOR AND ORDNANCE REPORTS OF NDRC 

1. Radio Proximity Fuze for Plane-to-Plane Rocket 
Application, Harry M. Diamond, W. S. Hinman, 
Jr., Robert D. Huntoon, Cledo Brunetti, and 
Chester H. Page, Service Projects OD-27 and 
OD-26, Report A-144, Feb. 12, 1943. 

Div. 4-211.1-M3 

2. Sampling Formulas for Qualifications and Proof 
Testing of Production Lots, T. N. White, OSRD 
3198, Memorandum A-82M, January 1944. 

Div. 4-770-MI 

3. Reports Pertinent to Early and Middle Function- 
ing of MC-382 Fuze, as follows: 

3a. A Study of the Relation between Afterburn- 
ing and Thyratron Voltage, R. Vorkink, Serv- 
ice Project OD-27, Memorandum Report 
158-T, Apr. 14, 1943. Div. 4-238.212-M3 

3b. Tests with Eccentric and with Non-Eccentric 
Powder, High-Angle Firing, R. Vorkink, 
Service Project OD-27, Memorandum Report 
338-T, June 1943. Div. 4-222.128-M11 

3c. Test for Ride Through with Various Powders 
and Firing Angles, R. Vorkink, Service 
Project OD-27, Memorandum Report 383-T, 
Aug. 5, 1943. Div. 4-222.128-M14 

3d. Fuze T6, Range, Dispersion, and Water Ap- 
proach Function, D. C. Friedman, Service 
Project OD-27, Memorandum Report 388-T, 
July 28, 1943. Div. 4-222.128-M13 

3e. Test of Effect of Velocity on Early Function- 
ing, R. Vorkink, Service Project OD-27, 
Memorandum Report 405-T, Aug. 12, 1943. 

Div. 4-222. 128-M15 

4. A Comparison of Several Makes of MC-382 Fuze 
with Respect to Early, Target and Late Functions 
and Duds, T. N. White, Memorandum Report 
220-T, May 13, 1943, and Supplement to A Com- 
parison of Several Makes of MC-382 Fuze with 
Respect to Early, Target and Late Functions and 
Duds, T. N. White, Service Project OD-27, Mem- 
orandum Report 282-T, June 10, 1943. 

Div. 4-222.128-M10 

REPORTS OF ORDNANCE DEVELOPMENT 
DIVISION OF NATIONAL BUREAU 
OF STANDARDS 

5. Reports pertinent to early and middle function- 
ing of the MC-382, as follows: 



458 


BIBLIOGRAPHY 


5a. Relation between Early Function and After- 
burning, T. N. White, Report OD-1-AB1, 
NBS, Ordnance Development Division, Mar. 

17, 1943. Div. 4-222. 129-M3 

5b. Effect of Powder Lot on Afterburning and 

Slivers, L. C. Miller, Report OD-1-AB2, 
NBS, Ordnance Development Division, Mar. 

18, 1943. Div. 4-411. 11-M2 

5c. The Effect of Powder Load on Afterburning 

and Slivers, L. C. Miller, Report OD-1-AB3, 
NBS, Ordnance Development Division, Mar. 
20, 1943. Div. 4-222.128-M4 

5d. Effect of Fin Structure on Early Function- 
ing, L. C. Miller, Report OD-1-AB4, NBS, 
Ordnance Development Division, Mar. 23, 
1943. Div. 4-222. 128-M5 

5e. Early Function Tests (1) Fuzes with Re- 
duced Sensitivity, (2) Motors with Metal 
Sweeps, L. C. Miller, Report OD-1-AB5, 
NBS, Ordnance Development Division, Mar. 
23, 1943. Div. 4-222.128-M6 

5f. Early Functions with MC-382 Fuze, Further 
Testing with Sweeps and with Powders, 
T. N. White, Report OD-1-AB6, NBS, Ord- 
nance Development Division, Mar. 27, 1943. 

Div. 4-222. 128-M7 
5g. Experiments on Early Functioning with 
Revere Motors (1) Soldering of Fin Retain- 
ing Rings, (2) Test of Powder Lot 9978, (3) 
Soldering of Fins in Open Position, L. C. 
Miller, Report OD-1-AB7, NBS, Ordnance 
Development Division, Mar. 31, 1943. 

Div. 4-411.2-M2 

5h. Static Tests on Afterburning (1) Use of 
Metal Sweeps, (2) Use of J P-26 5 Powder, 
L. C. Miller, Preliminary Report OD-1-AB8, 
NBS, Ordnance Development Division, Mar. 
29, 1943. Div. 4-411. 11-M3 

5i. Progress Report on Afterburning , H. F. 
Stimson, Progress Report OD-1-AB9, NBS, 
Ordnance Development Division, Apr. 9, 
1943. Div. 4-411. 11-M4 

5j. High-Angle Firing with MC-382 Fuzes 
[ Part ] A. Early Function Tests (1) Detun- 
ing of Units (2) Use of Sweeps and Plugs; 
[ Part] B. Tests of Mechanical SD Switches, 
L. C. Miller, Final Report OD-1-AB11, NBS, 
Ordnance Development Division, Apr. 17, 
1943. Div. 4-222. 128-M8 

5k. Incidence of Early Functions with POD 
Type Fuzes and MC-382 Fuzes: Compari- 
sons Based on Target Function and High- 
Angle Firing Tests, T. N. White, Report 
OD-1-AB12, NBS, Ordnance Development 
Division, May 1, 1943. Div. 4-222.129-M4 
51. Tests of Sweeps and Plugs, R. Vorkink, Re- 
port OD-1-AB13, NBS, Ordnance Develop- 
ment Division, May 7, 1943. 

Div. 4-222.128-M9 


5m. High-Angle Night Firing with Powders 
A-20, A-21, and A-22: Afterburning , Burn- 
ing Distances, H. F. Stimson, Report OD-1- 
AB14, NBS, Ordnance Development Di- 

vision, May 13, 1943. Div. 4-411. 11-M5 
5n. RC Delay Added to SW-200 Arming 

Switches, Effect on Early Functioning of 
MC-382 Fuzes, T. N. White, Report OD-1- 
AB15, NBS, Ordnance Development Di- 

vision, Sept. 14, 1943. Div. 4-222.128-18 
5o. Tests for Early Functioning with Different 
Powder Weights, R. Vorkink, Report OD-1- 
AB16, NBS, Ordnance Development Di- 

vision, Aug. 26, 1943. Div. 4-222.128-M16 
5p. Test for Mal-Functions of MC-382 with 
Special Fin Motors (No Locking Burr), R. 
Vorkink, Report OD-1-1, NBS, Ordnance 
Development Division, Sept. 2, 1943. 

Div. 4-222. 128-M17 
5q. Tests on Early Functioning of MC-382 
Fuzes [Part] A. Use of Purge Pellets; 
[ Part ] B. Increased Surface Area of Pro- 
pellant, L. C. Miller, Report OD-1-5, NBS, 
Ordnance Development Division, Sept. 14, 
1943. Div. 4-222. 128-M19 

5r. Effect of Propellant on Early Functioning 
[Part] A. Amount of Regular Propellant ; 
[Part] B. Special Propellant; [Part] C. 
Purge Pellets, T. N. White, Report OD-1-8, 
NBS, Ordnance Development Division, Sept. 
21, 1943. Div. 4-222. 128-M21 

5s. Test of Propellant Charge on Early Func- 
tioning, R. Vorkink, Report OD-1-13, NBS, 
Ordnance Development Division, Sept. 20, 
1943. Div. 4-222. 128-M20 

5t. Test of Effect of Purge Pellets on Early 
Functioning, R. Vorkink, Report OD-1-17, 
NBS, Ordnance Development Division, Sept. 
30, 1943. Div. 4-222.128-M22 

5u. Early Functioning of MC-382 Fuzes, Purge 
Pellet Field Test 5, L. C. Miller, Report OD- 
1-22, NBS, Ordnance Development Division, 
Oct. 6, 1943. Div. 4-222.128-M23 

5v. Early Functioning of MC-382 Fuzes, Purge 
Pellet Field Tests 6 and 7, L. C. Miller, Re- 
port OD-1-24, NBS, Ordnance Development 
Division, Oct. 13, 1943. Div. 4-222.128-M24 
5w. MC-382 Fuze Performance as Affected by 

Motors with Non-Locking Type Fins, T. N. 
White, L. C. Miller, and R. Vorkink, Report 
OD-1-27, NBS, Ordnance Development Di- 
vision, Oct. 15, 1943. Div. 4-222.128-M25 
5x. MC-382 Fuze Performance as Affected by 

Motors with Fins Welded into the Opened 
Position, D. C. Friedman, Report OD-1-40, 
NBS, Ordnance Development Division, Nov. 
4, 1943. Div. 4-222.128-M26 

5y. Early Functioning of MC-382 Fuze, Purge 
Pellet Field Test 8 (Also Tests with POD 



BIBLIOGRAPHY 


459 


Type Fuzes and with Pressure-Control 
Valves ), T. N. White and R. Vorkink, Re- 
port OD-1-42, NBS, Ordnance Development 
Division, Nov. 19, 1943. Div. 4-222.128-M27 
5z. Purge Pellet Test 9 Including Test of (1) 
Combination of Motors and Propellants, (2) 

A New Salted Powder, (3) Pressure-Control 
Valves, R. Vorkink, Report OD-1-59, NBS, 
Ordnance Deevlopment Division, Nov. 23, 

1943. Div. 4-222. 128-M28 

5aa. High-Angle Test of MC-382 Units to Deter- 
mine Propellant-Motor Combination for 
Acceptance Testing, D. C. Friedman, Report 
OD-1-119, NBS, Ordnance Development Di- 
vision, Jan. 26, 1944. Div. 4-222.128-M29 

5bb. Field Test of Eight Lots of Pellets, R. Vor- 
kink, Report OD-1-125, NBS, Ordnance De- 
velopment Division, Jan. 29, 1944. 

Div. 4-222. 128-M30 
5cc. Test of T 5 and T6 on Motors with Spring - 
Operated Fins, D. C. Friedman, Report OD- 
1-171, NBS, Ordnance Development Division, 

Feb. 26, 1944. Div. 4-222.123-MI 

odd. Test to Compare Performance of Type S 
(BRLG-6 Amplifier) and Standard MC-382 
Units, R. Vorkink, Report OD-1-189, NBS, 
Ordnance Development Division, Mar. 8, 

1944. Div. 4-222.128-M31 
See. Comparison of Performance of Type S and 

Standard MC-382 on Motors with Scallop- 
Type Traps, R. Vorkink, Report OD-1-197, 

NBS, Ordnance Development Division, Mar. 

15, 1944. Div. 4-222. 128-M32 

off. Early Functioning of T5 Units, Tests of 
Powder Lots, Motor Lots, Igniters, Traps, 

D. W. Scott and T. N. White, Report OD-1- 
227, revised Sept. 22, 1944. 

Div. 4-222.121-M6 
5 gg. Further Testing with Pellets and Salted 
Powders, D. W. Scott, Report OD-1-241, 

NBS, Ordnance Development Division, Apr. 

18, 1944. Div. 4-222. 128-M33 

Shh. Effect of Trap Structure on Early Function- 
ing of T 5 Fuzes, D. W. Scott, Report OD-1- 
253, NBS, Ordnance Development Division, 

Apr. 22, 1944. Div. 4-222.128-M34 

5ii. Effect of Fins on Mai-Functioning of T6 
Fuze, D. W. Scott, Report OD-1-259, NBS, 
Ordnance Development Division, Apr. 25, 

1944. Div. 4-222. 122-MI 

5jj. Effect of Salted Powder on Performance of 
MC-382 Fuzes, D. W. Scott, Report OD-1- 
274, NBS, Ordnance Development Division, 

May 3, 1944. Div. 4-222.128-M35 

5kk. Test of T6 Fuzes on Rigid-Fin Projectiles, 7. 
D. W. Scott, Report OD-1-280, NBS, Ord- 
nance Development Division, May 15, 1944. 

Div. 4-222.122-M2 8. 

511. Effect of Notched-Powder Loads on MC-382 


Functioning , D. W. Scott, Report OD-1-287, 
NBS, Ordnance Development Division, May 
27, 1944. Div. 4-222.128-M36 

5mm. Field Test of T5 on Projectiles with Bubble- 
Wire Traps, D. W. Scott, Report OD-1-368, 
NBS, Ordnance Development Division, June 
19, 1944. Div. 4-222. 121-MI 

5nn. Test of T 5 and T6 on Projectiles with Loose 
Joints, D. W. Scott, Report OD-1-395, NBS, 
Ordnance Development Division, July 8, 
1944. Div. 4-222.123-M2 

5oo. Test of T5 on Projectiles with Crimped and 
Brazed Fins, D. W. Scott, Report OD-1-403, 
NBS, Ordnance Development Division, July 
17, 1944. Div. 4-222. 121-M3 

5pp. Test of T 5 on Projectiles with Salted Powder 
and Bubble-Wire Traps, D. W. Scott, Report 
OD-1-397, NBS, Ordnance Development Di- 
vision, July 10, 1944. Div. 4-222.121-M2 
5qq. Performance of T 6 with 10 A Amplifiers on 
M9, M9A1 and M9A2 Motors, D. W. Scott, 
Report OD-1-404, NBS, Ordnance Develop- 
ment Division, July 21, 1944. 

Div. 4-222. 128-M37 
5rr. Effect of Bayonet and Bag Igniters on Func- 
tioning of T5 Fuze, D. W. Scott, Report OD- 
1-408, NBS, Ordnance Development Di- 
vision, July 19, 1944. Div. 4-222.121-M4 
5ss. High-Angle Test of T 5 with 10 A Amplifier 
(Some Shaker-Tested) on Motors with 
Hand-Crimped Fins, Straightened and Un- 
straightened, D. W. Scott, Report OD-1-423, 
NBS, Ordnance Development Division, July 
27, 1944. Div. 4-222.128-M38 

5tt. Performance of Shaker-Tested T5 with 10 A 
Amplifier, D. W. Scott, Report OD-1-477, 
NBS, Ordnance Development Division, Aug. 
24, 1944. Div. 4-222.128-M39 

5uu. T5 on M9A1 with Clamp-On Fixed Fins, 
D. W. Scott, Report OD-1-486, NBS, Ord- 
nance Development Division, Sept. 5, 1944. 

Div. 4-222. 121-M5 
5vv. Flight Test of T 5 Fuzes on T22 Rockets with 
EJA Propellant, D. W. Scott, Report OD-1- 
614, NBS, Ordnance Development Division, 
Jan. 4, 1945. Div. 4-222.121-M8 

5xx. Effect of Trap Length on Incidence of Early 
Functions in the T5, D. W. Scott, Report 
OD-1-691, NBS, Ordnance Development Di- 
vision, Mar. 29, 1945. Div. 4-222.121-M12 
6. Salvo Firing in Search of Sympathetic Function- 
ing of the MC-382, T. N. White, Report OD-1-15, 
NBS, Ordnance Development Division, Sept. 25, 
1943. Div. 4-245-MI 

Rotation of M9A1 with Hand-Crimped Fins, D. W. 
Scott, Report OD-1-588, NBS, Ordnance Develop- 
ment Division, Dec. 18, 1944. Div. 4-412. 2-M3 
Effect of Rocket Spin upon the Performance of 
VT Fuzes TU, T5, T6, Theodore B. Godfrey, Re- 


460 


BIBLIOGRAPHY 


port OD-1-668, NBS, Ordnance Development Di- 
vision, Mar. 13, 1945. Div. 4-222.123-M3 

9. Effect of Rain upon the Performance of VT 
Fuzes , T5 and T6, Theodore B. Godfrey, Report 
OD-1-669, NBS, Ordnance Development Division, 
Mar. 13, 1945. Div. 4-222.123-M4 

10. Effect of Rocket Spin on T5 Performance , D. W. 
Scott, Report OD-1-677, NBS, Ordnance Develop- 
ment Division, Mar. 21, 1945. Div. 4-222.121-M9 

11. Effect of Rocket Spin on T5 Arming Distance, 
D. W. Scott, Report OD-1-678, NBS, Ordnance 
Development Division, Mar. 21, 1945. 

Div. 4-222. 121-M10 

12. Arming Time of T5 on T22 Fired Spiral Launcher, 
D. W. Scott, Report OD-1-689, NBS, Ordnance De- 
velopment Division, Mar. 28, 1945. 

Div. 4-222. 121-Mil 

13. Effect of Rotation Upon the Operation of the SW- 

230 Switch, Charles C. Gordon, Report OD-1-729, 
NBS, Ordnance Development Division, Apr. 30, 
1945. Div. 4-238. 511-M6 

14. Ballistic Test, MU3C Shell with Various Fuzes, G. 
Rabinow, Report OD-1-737, NBS, Ordnance De- 
velopment Division, May 8, 1945. Div. 4-514-M3 

15. Field Test of 1U0 Philco T91 and 120 Emerson T92 
— Various Release Conditions, Army Ordnance 
Test, R. Vorkink, Report OD-1-825, NBS, Ord- 
nance Development Division, July 9, 1945. 

Div. 4-222. 114-M2 

16. High-Angle and Target Test of T5 and T50 on T22 
Rockets Modified for Helical Launcher, B. M. 
Bennett, Report OD-1-895, NBS, Ordnance De- 
velopment Division, Oct. 8, 1945. 

Div. 4-222. 129-M5 

17. Afterburning from Rocket Motors and Malfunc- 
tioning of VT Fuzes (Summary Report), H. F. 
Stimson, Report OD-1-896, Oct. 15, 1945. 

Div. 4-411. 11-M6 

18. Summary of Experimental Field Test Results of 
Bomb Fuzes by Test Request Number, Ordnance 
Analytical Group, Report OD-2-224, NBS, Ord- 
nance Development Division. Div. 4-222.1 1-Ml 

19. Summary of Pre-Production Mortar Fuze Field 
Test Results, Ordnance Analytical Group, Report 
OD-2-229, NBS, Ordnance Development Division, 
June 18 and Sept. 27, 1945. Div. 4-222. 131-M4 

20. Mortar Fuze Arming Time Tests, Ordnance Ana- 
lytical Group, Report OD-2-230, NBS, Ordnance 
Development Division, June 23 and July 14, 1945. 

Div. 4-222.131-M5 

21. Summary of Rocket Fuze Plane Firing (Air-to- 

Earth) Tests, Ordnance Analytical Group, Re- 
port OD-2-269, NBS, Ordnance Development Di- 
vision, Aug. 24, 1945. Div. 4-222.126-M3 

22. Arming of VT Fuzes: Analysis and Measurement 

of Spread in Air-Trav el-to- Arming , A. L. Leiner, 
Report OD-2-275, NBS, Ordnance Development Di- 
vision, Mar. 14, 1946. Div. 4-244.1-M3 

23. Arming Considerations in T6, Bertrand J. Miller 


and Philip R. Karr, Report OD-3-74, NBS, Ord- 
nance Development Division, Jan. 22, 1944. 

Div. 4-238.515-MI 

24. Minimum Useful Range for T6, Robert D. 
Huntoon, Report OD-3-98, NBS, Ordnance De- 
velopment Division, Feb. 9, 1944. 

Div. 4-238. 515-M2 

25. Computation of Burst Heights of Longitudinally - 

Excited Bomb Fuzes. R. B. Schwartz, Report OD- 
3-281, NBS, Ordnance Development Division, Aug. 
7, 1945. Div. 4-241-M8 

26. Summary of Rocket Fuze Experimental Field Test 
Results, Analytical Group, Paul F. Bartunek and 
C. F. Smolen, Report OD-7-97M, NBS, Ordnance 
Development Division, Apr. 2, 1945. 

Div. 4-222. 12-MI 

27. Summary of Recent Target Tests at Blossom 

Point, Alex Orden and C. F. Smolen, Report OD- 
7-98, NBS, Ordnance Development Division, Apr. 
9, 1945. Div. 4-222. 12-M2 

28. Analysis of Variations in the Spread of Air- 

Trav el-to- Arming , B. M. Bennett, Report OD-7- 
103, NBS, Ordnance Development Division, Apr. 
11, 1945. Div. 4-244.1-M2 

29. Summary of Tests of T30 and T200U Rocket Fuzes 

during the Period November 30, 19 UU to March 
31, 19 U5, Paul F. Bartunek, Report OD-7-108, 
NBS, Ordnance Development Division, Apr. 30, 
1945. Div. 4-222.126-MI 

30. Mortar Fuze Field Test Results, Experimental 

Tests by Test Request, Analytical Group, Paul F. 
Bartunek and C. F. Smolen, Report OD-7-112, 
NBS, Ordnance Development Division, Apr. 23, 
1945. Div. 4-222. 133-Ml 

31. Tests BJM-5 and BJM-6, Charles Ravitsky, 
Progress Report OD-7-206R, NBS, Ordnance De- 
velopment Division, May 14, 1945. 

Div. 4-222. 124-M3 

MEMORANDA OF ORDNANCE DEVELOPMENT 
DIVISION, NBS 

32. Mid-Functioning, Section 1 Memo to Harry M. 
Diamond from H. F. Stimson, NBS, Ordnance 
Development Division, June 5, 1944. 

Div. 4-222. 122-M3 

33. Prediction of T51 Burst Height, D. 1 . Worcester 
Technical Memorandum OD-l-TM-11, NBS, Ord- 
nance Development Division, Nov. 8, l$4o 

Div. 4-241-M9 

34. Relation between the Spread in Burst Heights 

and the Mean Burst Height of VT Bomb Fuzes, 
R. C. Stillinger, Technical Memorandum OD-1- 
TM-13, NBS, Ordnance Development Division, 
Dec. 13, 1945. Div. 4-241-M10 

35. Empirical Burst Height Distribution Formulae 
for VT Bomb Fuze, R. C. Stillinger and Irene 
Hess, Technical Memorandum OD-l-TM-23, NBS, 
Ordnance Development Division, Sept. 17, 1946. 

Div. 4-241-M11 



BIBLIOGRAPHY 


i 


461 


36. A Comparison of Observed and Predicted Burst 

Heights of Ring-Type VT Bomb Fuzes, W. J. 
Cronin and T. N. White, Technical Memorandum 
OD-1-24M, NBS, Ordnance Development Division, 
Sept. 19, 1946. Div. 4-241-M12 

37. Analysis of T30 and T200U FOMA Tests, F. L. 
Celauro, Memorandum OD-2-272M, NBS, Ord- 
nance Development Division, Sept. 19, 1946. 

Div. 4-126-M4 

REPORTS OF CONTRACTORS OF DIVISION 3 
(SECTION L) OF NDRC 

38. Trajectories of Aircraft Rockets 3.5" and 5.0", 

OSRD 2225, OEMsr-418, Service Projects OD-162, 
OD-164, and NC-170, Division 3 Report CIT UBC 
27, California Institute of Technology, Sept. 25, 
1944. Div. 4-412. 1-M2 

REPORTS OF CONTRACTORS OF 
DIVISION 4, NDRC 

39. Final Report: Summary Technical Paper, State 

University of Iowa Staff, Contract OEMsr-769, 
Sept. 29, 1945. Div. 4-100-M7 

REPORTS OF APPLIED MATHEMATICS PANEL 

40. Probability that a U.5" Rocket Fired from Astern 

Will Destroy a Twin-Engine Bomber (Ju-88) as a 
Function of the Point of Burst, Statistical Re- 
search Group, Columbia University, AMP Report 
21. 1R, July 1944, and Optimum Burst Surface for 
U.5" Airborne Rocket Fired from Astern at Twin- 
Engine Bomber (Ju-88), AMP Report 21.2R, 
Statistical Research Group, Columbia University, 
July 1944. Div. 4-412.3-MI, Div. 4-412.3-M2 

41. Effectiveness of a U-5" Airborne Rocket with T5 
Fuze when Fired at Twin-Engine Bomber from 
Astern, AMP Report 21. 3R, Statistical Research 
Group, Columbia University, July 1944. 

Div. 4-412.3-M3 

U. S. MILITARY PUBLICATIONS 

Navy 

42. Final Report on Air-to-Air Firing of Mk-171 
Mod 0 Fuzes in 3.5" and 5.0" AR, NOTS Project 
104 AFS, Serial 52, Aug. 5, 1945. 

43. Final Report on Air-to-Ground Firing of Mk-172 
Mod 0 Fuzes with 5.0" AR, NOTS Project 106 AF, 
May 3, 1945. 

Army 

44. Proof Testing — A Brief Statistical Description of 
Final Acceptance Sampling Formulas and Prov- 
ing Ground Test Performance, W. Steele and E. J. 
Fister, Camp Evans Signal Laboratory, Technical 
Memo SA-Q1, Feb. 3, 1945. 

45. Second Interim Report on Test of Fuzes, Bomb, 
T50, Army Air Forces Board (Eglin Field, 


Florida), Project F4012 (Test S.T. 1-44-12), Mar. 
29, 1945. 

46. Final Report on Test of Napalm-Gasoline Filled 
M-10 Tanks with T50 and T51 Fuzes for Use 
as an Incendiary Bomb, Army Air Forces Board 
(Eglin Field, Florida), Project F4222 (Test S.T. 

1- 44-91), Apr. 20, 1945. 

47. Final Report on Comparison of the Effectiveness 
of Bombs against Enemy Installations, Army Air 
Forces Board (Eglin Field, Florida), Project 
F4475 (Test S.T. 1-45-19), May 14, 1945. 

48. Supplemental Test on Aircraft Rockets for Anti- 
Personnel Effect, Army Air Forces Board (Eglin 
Field, Florida), Project 4514 C471.94 (Test S.T. 

2- 45-16) Sept 4, 1945. 

49. Test of Fuze, Bomb, Nose T51E1, Army Air Forces 
(Eglin Field, Florida), S.T.P 1-45-6, Nov. 27, 
1945. 

50. First Partial Report of Test of U-5-Inch Rockets 
and Rocket Launcher, T-18E2 and T-20, Field 
Artillery Board, Fort Bragg, N. C., Jan. 17, 1944. 

51. Procedure for Conducting Field Engineering Ac- 
ceptance Tests of Metal Parts Assentblies of VT 
Bomb Fuzes, L. L. Parker, Apr. 3, 1945. 

52. Tentative Specification, Ordnance Department, 
AXS-1603, May 9, 1945. 

53. Procedure for Conducting Field Engineering Ac- 
ceptance Tests of Metal Parts Assemblies of VT 
Fuze T200U, Army Ordnance Specifications, May 
11, 1945. 

54. Procedure for Conducting Field Engineering Ac- 
ceptance Tests of Metal Parts Assemblies of VT 
Fuze T200U, Army Ordnance Specifications, Aug. 
3, 1945. 

55. Army Ordnance Specifications AXS-1603 (Re- 
vision 1), Aug. 13, 1945. 

SUBDIVISION OF REFERENCES 

56. In reference 26 the following test numbers: TBG- 
93, -111, -115, -122A, -122B, -127, -130C, RQ-1C. 

57. In reference 26 the following test numbers: TBG- 
114, -120, -123, -124, -125, -128, RQ1A, RX2. 

58. In reference 26 the following test numbers: TBG- 
80, -90, -105, -131, -132, RX1A. 

59. In reference 26 the following test numbers: TBG- 
91, -94, -101, -105. 

60. In reference 26 the following test numbers: TBG- 
82, -86, -87, -88, -93, -103. 

61. In reference 26 the following test numbers: TBG- 
107, -108, -109A, -110, -113, -116, -117, -121, -126, 
-130A. 

62. In reference 26 the following test number: TBG- 
130B. 

63. In reference 26 the following test number: TBG- 
109B. 

64. In reference 26 the following test number: TBG- 
113. 

64a. In reference 26 the following test number: 

TBG-85B. 



462 


BIBLIOGRAPHY 


64b. In reference 26 the following test numbers: 

TBG-112, 0118, -119. 

65. In reference 18 the following test numbers: CB- 

257, -270, -271, -272, -285, -301, -323, -324, -341, 

-358, -389, -396, -414, -419, -420, -423, -431, -434, 

-435, -445, -446, -448, -451, -452, -453, -454, -458, 

-460, -462, -472, -474, -478, -483, -499, -500, -508, 

-509, -518, -523, -527, SC-5, -9, -10, -12, -13, -14, 
-15, -16, -17, -19, -20, PX-10, BX-4, -5. 

66. In reference 18 the following test numbers: CB- 
468, -491, -493, -501, -504, -506, -511, -515, -517, 
-526, BX-1. 

67. In reference 18 the following test number: CB- 
506. 

68. In reference 18 the following test numbers: CB- 
468, -475, -491, -501, -515, BX-1. 

69. In reference 18 the following test numbers: CB- 
493, -504, -511, -517, BX-1. 

70. In reference 18 the following test numbers: CB- 
410, -416, -476, -502, PX-5, SC-7. 

71. In reference 18 the following test numbers: CB- 
344, -354, -376, -386, -489, -522, CEX-5, -7, BX-6. 

72. In reference 18 the following test numbers: CB- 
482, -485, -486, -487, -495. 

73. In reference 18 the following test numbers: CB- 
266, -349, -359, LSP-1, Ordnance Test (Aberdeen). 

74. In reference 18 the following test numbers: CB- 
487, -495, -514, -516, -522, BX-6. 

75. In reference 18 the following test numbers: CB- 
485, -486, -489, -495. 

76. In reference 18 the following test numbers: CB- 
475, -476, -489, -502. 

77. In reference 18 the following test numbers: CB- 
283, -284, -286, -289, -290, -291, -292, -294, -295, 
-297, -299, -300, -304, -305, -307, -309, -310, -311, 
-313, -314, -326, -327, -328, CHP-20, -21. 

78. In reference 18 the following test numbers: CB- 
475, -476, -482, -485, -486, -487, -495, -502, -515. 

79. In reference 18 the following test numbers: CB- 
344, -354, -386, -410, -416, -468, -482, -485, -486, 
-487, -489, -491, -493, -495, -501, -504, -506, -511, 
-515, -517, -522, -526, PX-5, SC-6, -7, CEX-5, -7, 
BX-1, -6. 

80. In reference 18 the following test numbers: CB- 
266, -349, -359, Dahlgren test of T91, Ordnance 
Test (Aberdeen). 

81. In reference 18 the following test numbers: CB- 

357, -360, -365, -369, -370, -371, -372, -373, -377, 
-378, -379, -387, -388, -393, -402, -404, -411, -412, 

-413, -417, -418, -421, -429, -430, -447, -450, -451, 

-455, -458, -459, -461, -463, -465, -469, -473, -477, 

-480, -488, -492, -497, -498, -500, -503, -513, -518, 

-521, BX-1, -3, -7, -8, -11, -13, -15, -17, -18. 

82. In reference 18 the following test numbers: CB- 
-458, -459, -469, -477, -479, -480, -488, -492, -498, 
-513, -518, -521, BX-3, -8, -11, -15, -18. 

83. In reference 18 the following test numbers: CB- 
369, -370, -371, -372, -425, -429, -447, -450, -451, 
-457, -461, -463, -464, -465, -481, -500, -503, -510, 
BX-1, -7, -16, -17. 


84. In reference 18 the following test numbers: CB- 
497, -500, -510. 

85. In reference 18 the following test numbers: CB- 

357, -360, -365, -370, -371, -372, -373, -381, -387, 

-388, -393, -398, -399, -401, -404, -411, -413, -417, 

-429, -447, -450, -451, -455, -458, -461, -465, -469, 

-473, -477, -480, -481, -488, -492, -497, -498, -500, 

-503, -513, -518, -529, BX-1, -3, -7, -8, -11, -15, -17, 
-18. 

86. In reference 18 the following test numbers: CB- 
473, -480, -492, -496, -497, -498, -500, -507, -513, 
-519, -525, BX-1, -3, -7, -8, -14, -15, -18. 

MISCELLANEOUS REFERENCES PERTAINING 
TO EFFECTIVENESS OF PROXIMITY FUZES 

87. “Trials with AN-M.64 Bombs, Nose Initiated 
(T-50) against Close Support Targets,” Ordnance 
Board Proceedings No. Q2881, E. S. Pearson and 
B. L. Welch, Dec. 13, 1944. 

88. “Bombs, Aircraft, and Fuzes, Bomb, Aircraft: (1) 
Report on test conducted in U. S. A.; (2) Theo- 
retical calculations on optimum height of burst of 
aircraft bombs fitted with V.T. fuzes.” Ordnance 
Board Proceedings No. Q3860; notes, E. S. Pear- 
son, Oct. 29, 1945. 

89. Airburst for Blast Bombs, E. B. Wilson, Jr., 
NDRC Report A-322, April 1945. 

90. Effect of Height of Detonation of Bombs on the 
Blast Pressures and Impulses of Surrounding 
Buildings, in Richmond Park 1/7 Square Model 
Town Tests, Road Research Laboratory, Depart- 
ment of Scientific and Industrial Research, Min- 
istry of Supply, Note No. MOS/434/RJ.EK, 
March 1945. 

91. “Air Burst Bombs,” Memorandum from A. H. 
Taub (Division 2, NDRC) to Col. P. Schwartz 
(Director of Armament, USSTAF), Dec. 21, 1944. 

92. “Air Burst Bombs — Status, as of 20 October 
1944,” D. G. Christopherson, Ministry of Home 
Security, REN-461. 

93. Note on Airbursts of 4,000-lb. H.C. Bomb with 
T-51 Fuze, F. H. East, Technical Note No. ARM- 
343, Royal Aircraft Establishment, April 1946. 

94. Interim Report, February 15 to March 7, 1945, 
A. V. Astin to Dr. Alexander Ellett. 

95. Inflammability of Mustard Chargings in British 
Bombs A/C LC 500-lb Mark II Equipped with T-51 
Fuzes, San Jose Project Report 71, June 23, 1945. 

96. Optimum Height of Setting for T-50 Fuze on Blast 
Bombs, A/C LC 500-lb Mark II Charged Dyed 
Methyl Scelicyliate and Dropped onto Jungle, 
San Jose, Project Report 69, Chemical Warfare 
Service, June 22, 1945. 

97. Multiple Bomb Assessment of Blast Bomb A/C 
LC 500-lb Mark II Fitted with T-51 Fuze and 
Charged HT When Dropped from High Altitudes 
into Jungle Terrain, San Jose, Project Report 73, 
Chemical Warfare Service, July 28, 1945. 

98. Statistical Tables for Biological, Agricultural and 
Medical Research, Fisher and Yates. 


SECRET^ 


OSRD APPOINTEES 

division 4 


Chief 

Alexander Ellett 


Technical Aides 

A. S. Clarke John S. Rinehart 

Sebastian Karrer E. R. Shaeffer 

Cathryn Pike A. G. Thomas 

R. M. Zabel 


Members 

L. J. Briggs Harry Diamond 

W. D. COOLIDGE F. L. HOVDE 

J. T. Tate 


Special Assistants 


M. G. Domsitz 
W. E. Elliott 
Wendell Gould 
W. S. Hinman, Jr. 


Joseph Kaufman 
J. L. Thomas 

E. A. Turner 

F. C. Wood 


Consultants 


A. V. Astin 
R. A. Becker 
R. M. Bowie 
Cledo Brunetti 
J. W. DuMond 
Saul Dushman 
Wm. Fondiller 
T. B. Godfrey 
L. R. Hafstad 
J. E. Henderson 
R. D. Huntoon 
J. A. Jacobs 
R. B. Janes 
T. Lauritsen 


D. H. Loughridge 
W. B. McLean 
F. L. Mohler 
S. H. Neddermeyer 
H. F. Olsen 
C. H. Page 
W. J. Shackelton 

F. B. SlLSBEE 

K. D. Smith 

G. W. Stewart 
J. F. Streib 

L. S. Taylor 
G. W. Vinal 
W. L. Whitson 


R. M. Zabel 



CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS 


Contract 

Number 

Name and Address of Contractor* 

Subject 

OEMsr-258 

Friez Instrument Division, Bendix Aviation 
Corporation 

Baltimore, Maryland 

Studies and experimental investigations in 
connection with continuous development 
work on special radio devices. 

OEMsr-343 

Westinghouse Electric and Manufacturing 
Company 

Baltimore, Maryland 

Studies and experimental investigations in 
connection with the development of 
special radio devices. 

OEMsr-500 

Western Electric Company, Inc. 

New York, New York 

Studies and experimental investigations in 
connection with the development of elec- 
tronic devices. 

OEMsr-528 

National Carbon Company, Inc. 

New York, New York 

Production of small batteries suitable for 
operation at low temperatures. 

OEMsr-611 

General Electric Company 

Schenectady, New York 

Studies and experimental investigations in 
connection with the development of mini- 
ature vacuum tubes, and report the re- 
sults thereof. 

OEMsr-566 

Raytheon Production Corporation 

Newton, Massachusetts 

Studies and experimental investigations in 
connection with the development of mini- 
ature vacuum tubes. 

OEMsr-630 

Sylvania Electric Products, Inc. 

Salem, Massachusetts 

Studies and experimental investigations in 
connection with the development of mini- 
ature vacuum tubes having a very low 
microphonic output. 

OEMsr-769 

University of Iowa 

Iowa City, Iowa 

Studies and experimental investigations in 
connection with development work on 
special electronic devices and associated 
equipment. 

OEMsr-866 

Philco Corporation 

Philadelphia, Pennsylvania 

Studies and experimental investigations in 
connection with the development of 
special radio devices and associated equip- 
ment. 

OEMsr-885 

Emerson Radio and Phonograph Corpora- 
tion 

New York, New York 

Studies and experimental investigations in 
connection with and carry on continuous 
development work on special radio de- 
vices and associated equipment. 

OEMsr-887 

Washington Institute of Technology 
Washington, D. C. 

Development of accessories for special elec- 
tronic devices and associated equipment. 

OEMsr-905 

Western Electric Company, Inc. 

New York, New York 

Studies and experimental investigations in 
connection with the development of 
special electronic devices. 

OEMsr-941 

Federal Telephone and Radio Corporation 
East Newark, New Jersey 

Studies and experimental investigations in 
connection with the development of 
special selenium rectifiers. 


* The National Bureau of Standards, which served as the central laboratories for Division 4, NDRC, did not operate under a contract 
but as a government agency on a direct transfer of funds from OSRD. 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS (Continued) 


Contract 

Number 

Name and Address of Contractor * 

Subject 

OEMsr-949 

University of Florida 

Gainesville, Florida 

Conduct theoretical studies and experi- 
mental investigations in connection with 
problems peculiar to special electronic de- 
vices for ordnance application. 

OEMsr-954 

The Zell Corporation 

Baltimore, Maryland 

Furnishing machining facilities in connec- 
tion with development of special elec- 
tronic devices. 

OEMsr-980 

Zenith Radio Corporation 

Chicago, Illinois 

Studies and experimental investigations in 
connection with development of special 
electronic devices. 

OEMsr-981 

Knapp-Monarch Company 

St. Louis, Missouri 

Studies and experimental investigations in 
connection with the development of 
special power supplies and associated 
equipment. 

OEMsr-1003 

Radio Corporation of America 

Harrison, New Jersey 

Studies and experimental investigations in 
connection with development of special 
miniature vacuum tubes. 

OEMsr-1106 

Westinghouse Electric and Manufacturing- 
Company 

Washington, D. C. 

Pilot production of special electronic de- 
vices. 

OEMsr-1109 

General Electric Company 

Schenectady, New York 

Studies and experimental investigations in 
connection with development work on 
special electrical and radio devices and 
associated equipment. 

OEMsr-1113 

Emerson Radio and Phonograph Corpora- 
tion 

New York, New York 

Manufacture and delivery of special elec- 
tronic devices. 

OEMsr-1117 

Globe-Union, Inc. 

Milwaukee, Wisconsin 

Studies and experimental investigations in 
connection with development of special 
electrical and mechanical devices. 

OEMsr-1133 

Zenith Radio Corporation 

Chicago, Illinois 

Manufacture and delivery of special elec- 
tronic devices. 

OEMsr-1134 

Knapp-Monarch Company 

St. Louis, Missouri 

Manufacture and delivery of special power 
supplies. 

OEMsr-1161 

The Rudolph Wurlitzer Company 

North Tonawanda, New York 

Studies and experimental investigations in 
connection with the development of 
special electronic devices. 

OEMsr-1163 

The Rudolph Wurlitzer Company 

North Tonawanda, New York 

Manufacture and delivery of special elec- 
tronic devices. 

OEMsr-1196 

Philco Corporation 

Philadelphia, Pennsylvania 

Manufacture and delivery of special elec- 
tronic devices. 


SECRET 


465 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS (Continued) 


Contract 

Number 

Name and Address of Contractor* 

Subject 

OEMsr-1227 

Bowen and Company, Inc. 

Bethesda, Maryland 

Furnish necessary machine shop and assem- 
bly facilities for the development of 
special electronic devices. 

OEMsr-1251 

General Electric Company 

Schenectady, New York 

Manufacture and delivery of special elec- 
tronic devices. 

OEMsr-1378 

Raymond Engineering Laboratory 

Berlin, Connecticut 

Studies and experimental investigations in 
connection with development of special 
electronic devices. 

OEMsr-1437 

The General Instrument Corporation 

Elizabeth, New Jersey 

Studies and experimental investigations in 
connection with development of electrical 
and mechanical devices. 

OEMsr-1477 

Zenith Radio Corporation 

Chicago, Illinois 

Development and production of special 
electronic devices. 

OEMsr-1500 

Emerson Radio and Phonograph Corpora- 
tion 

New York, New York 


OEMsr-1501 

Solar Aircraft Company 

San Diego, California 

Design and produce donut-type setback 
arming devices for use on British rockets 
equipped with VT fuzes. 


466 


SECRET 


/ 


SERVICE PROJECT NUMBERS 

The projects listed below were transmitted to the Executive 
Secretary, NDRC, from the War or Navy Department through 
either the War Department Liaison Officer for NDRC or the 
Office of Research and Inventions (formerly the Coordinator of 
Research and Development), Navy Department. 


Service 


Project 


Number 

Subject 


Chemical Warfare Service 

CWS-19 Development of an influence fuze for airplane spray apparatus. 
Ordnance Department 

OD-27 Development of proximity (influence) fuzes for bombs and 
projectiles. 

OD-191 Development of VT fuze and UHF and VHF circuit techniques. 
OD-192 Development of counter-countermeasures for VT fuzes. 


SC-38 

SC-40 


Signal Corps 

Field testing equipment for proximity fuzes. 
Substitute for dry battery BA-55. 


467 



I 


I 

INDEX 

The subject indexes of all STR volumes are combined in a master index printed in a separate volume. 

For access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


A-l mortar shell retrieving device, 355- 
357 

A-2 mortar shell retrieving device, 356- 
357 

Acceleration integrators for arming prox- 
imity fuzes, 171-174 
British type, 172 
double action arming device, 173 
for T-4, T-5 and T-6 fuzes, 172 
Acceptance testing, requirements, 428- 
432 

Navy rocket fuzes, 430-431 
T-5 fuzes, 431-432 
VT bomb fuzes, 428-430 
Active-type fuzes, 4-5 
Afterburning in rockets 
Ballistite burning, 364-365 
burning process, 364-365 
definition, 211 

pellets added to Ballistite, 365 
salted powder additions, 366 
summary, 336 

trap ring variations, 365-366 
with T-30 fuze, 380-382 
with various propellants, 337 
Air-burst bombs, effectiveness, 412-416 
against moderately shielded person- 
nel, 412-413 

against shielded personnel and un- 
shielded materiel, 413-414 
against unshielded materiel and en- 
trenched personnel, 414 
blast effect, 415-416 
compared with contact-burst bombs, 
414 

spread of gas, 416 
Air-burst fuzes, effectiveness, 14-15 
Aircraft, reflecting properties, 61-64 
effect of wavelength, 64 
experimental measurement, 61-63 
sensitivity requirements for plane-to- 
plane rocket fuze, 63-64 
Air-travel devices for safety in arming 
fuzes, 169 

Allis-Chalmers Company, fuze bear- 
ings, 190 

Alnico rotors for fuze generators, 269 
Alternator, permanent magnet, 146-147 
American Phenolic Corporation, ther- 
mosetting cement, 248 
Amphenol 912 cement, 248, 252 
Amplifier systems, 103-117, 256-265 
adjustment and testing, 115 
ceramic amplifiers, 259 
disk construction, 259 
potting and impregnating, 261-265 


properties of pentodes, 114-115 
requirements, 103-104, 256 
response to spurious signals, 115-116 
ring construction, 259 
sandwich construction, 257-258 
tolerance of components and varia- 
tion in performance, 116-117 
Amplifier systems, characteristics, 104- 
110 

for airborne target, longitudinal ex- 
citation, 105-106 

for ground approach, longitudinal 
excitation, 106-108 
for ground approach, transverse ex- 
citation, 108-110 
Amplifier systems, gain, 110-114 
axial antenna fuzes, 110-111 
combination amplifiers, 113-114 
gain-control condensers, 261 
transverse-antenna fuzes, 112-113 
Angle of approach, rocket, 339-340 
Antenna 

constant, evaluation, 75-77 
fuze, axial, 110-111 
fuze, transverse, 30-32 
noise from propellant flames, 72-75 
noise resulting from geometric de- 
formations, 71-72 

reflectors, use as signal simulators, 
66-67 

size limitations, 167 
Antenna and target, interaction phe- 
nomena, 22-24 

fundamental equations, 22-23 
fuze equations, 23-24 
fuze problem as interaction of two- 
terminal networks, 22 
Antenna impedance, 17-22, 37-43 
approximations in impedance repre- 
sentation, 19-21 

ground-approach case, magnitude and 
frequency of impedance signal, 
51-54 

ground-approach case, prediction of 
height of function, 50-51 
impedance concept, 21-22 
input impedance, 23 
radiation resistance, 38-43 
reactance across antenna terminals, 
39-40, 41-43 

reflected wave or doppler frequency 
concept, 18 

reflection equivalent to change of 
antenna impedance, 18-19 
specification of antenna terminals, 
37-38 

SECRET 


Antenna impedance, airborne target, 
59-64 

properties of impedance signal wave, 
59-61 

reflecting properties of aircraft, 61-64 
Antenna impedance modulation, cir- 
cuit response, 34-37 
differential signals, 34-35 
finite signals, 35 
fuze circuit parameters, 35-37 
Antennas, transverse, 48-49 
Antiaircraft use of fuzes, summary, 14- 
15 

Antimateriel bomb fuzes, military re- 
quirements, 3 
Apex firing test, 296 
AR 5.0 Navy rocket fuze, 217-220 
amplifier, 220 
amplifier gain, 237 
AR rocket, characteristics, 326 
arming mechanism, 219 
burst height, 219, 237 
characteristics, 235 
firing circuit, 220 
limitations, 218 
military requirements, 217 
power supply, 220 
radiation pattern, 237 
release altitude, 236 
r-f system, 220 
safety and arming, 218 
Arming methods 

acceleration integrators, 171-174 
air-travel devices, 169, 388, 393-394 
arming delay, 212 
arming pulse, 99, 296 
arming wire, 169 
clocks and timing devices, 170 
dashpot arming device, 192 
“doughnut” mechanism, 187 
effect of air pressure, 170 
effect of propellant temperature, 336 
electric arming, 125-130 
for accelerated projectiles, 212 
for battery-powered rocket fuze, 159- 
160 

for bomb fuzes, 224-225, 321-322, 
387-394 

for mortar shell fuzes, 418-419 
for nonaccelerated projectiles, 212 
for rocket fuzes, 159-160, 333-335 
manual arming, 169 
RC arming, 125-129, 335 
safety features, 212 
Army 4.5-in. rocket fuzes 
see 4.5-in. Army rocket fuzes 


469 


470 


INDEX 


Audio portion of fuze 
function, 284 
input circuits, 284-285 
output circuits, 285-286 
production testing, 302-304 
signal simulator, 69-70 
tests, 284-287 
thyratron tests, 286-287 

BA-55 battery pack, 136-138 

Ball bearings for proximity fuzes, 178 

Ballistics of rocketry 

angle of approach, 339-340 
rate of spin, 340 
velocity and acceleration, 339 
yaw, 340 

Ballistite burning in rockets, 364-365, 
380-381 

Bar-type bomb fuzes, 221-228, 405-412 
see also T-51 fuze; T-82 fuze 
amplifier, 226 

burst height, 224, 407, 411-412 
delayed arming device, 410-411 
description, 221-222 
effect of release conditions, 408-409, 
411 

effect of vehicle, 408, 411, 412 
guide plates, 410 
properties, 228 
reliability, 223 
summary, 221, 407-408 
testing conditions and devices, 282- 
283, 406-407 

train release, 408-409, 410 
washers, 409-410 
yellow carrier, 234 
Batteries for fuzes 
dry, 133, 136-138 
reserve, 133-134, 138-140 
vibrator, 134 
Battery fuzes 
see also T-5 fuze 
arming mechanism, 176 
detonators, 177 
head, 176 
MC-382; 92 

mechanical design, 175-177 
rocket fuzes, 158-160 
switch contacts, 177 
BC (battery command) telescope, 345 
Bell Telephone Laboratories, P-4 771B 
bomb fuze, 199 
Bomb fuzes 
amplifier, 226 

arrangement of components, 224 
burst heights, 224, 230 
directional sensitivity, 6-7 
firing circuit, 227 

military requirements, 2-3, 220-221 
oscillator assemblies, 225 
P-4 771B fuze, 198 


✓ 


plastic and metal vanes, 142-143 
power supply, 227 
production data, 228, 229 
reliability, 223 
r-f system, 222, 225 
safety, 222-223, 225 
specific applications, 222 
train-bombing, 322-323 
Bomb fuzes, arming, 387-394 
air travel, 169, 388, 393-394 
arming wire, 169 
effect of bomb, 388 
effect of plane speed, 388 
effect of release altitude, 388 
mean air travel vs\ rotor setting, 391- 
393 

MinSAT settings, 389-390 
reasons for study, 388 
release methods, 389 
rotor setting, 388-389, 393-394 
tests, 321-322, 390-391 
vane speed variations, 393 
Bomb fuzes, specific models 

see also T-50 fuze; T-50E1 fuze; 
T-50E4 fuze; T-51 fuze; T-82 
fuze 

T-40; 3, 198 
T-43; 3, 198 

T-51E1; 234, 409-410, 422-426 
T-89; 10, 13, 229, 396-397 
T-90; 13, 232, 398 
T-91; 10, 13, 229, 397 
T-91E1; 397-398 
T-92; 10, 13, 232 
T-92E1; 232, 398 
Bomb fuzes, tests, 313-324 
arming tests, 321-322 
assembly of components, 314-315 
bomb preparation, 314 
bomb types tested, 313-314 
dive tests, 323 
function heights, 317-318 
function time, 318-319 
fuze carrier characteristics, 319-321 
phonographic determination of func- 
tion time, 319 

photographic determination of func- 
tion heights, 317-318 
plane-to-ground communications, 315 
purpose, 313 
range layout, 315-316 
time lags, determination, 323-324 
train tests, 322-323 
Bomb fuzes, types 
air-burst bomb fuzes, 412-416 
bar-type, 221-228, 405-412 
general types, 221 
generator-powered fuzes, 160-165 
ring-type, 223-229, 232, 394-405 
vane types, 223 



British 

acceleration-operated arming device 
for fuzes, 172 

HC (high-capacity) bombs, 415-416 
Brown carrier fuzes 
amplifier gain, 229 
bomb fuzes, 229 
burst heights, 230 
performance, 400 
radiation patterns, 231 
ring-type, 235 
rocket fuzes, 240 
“Burst,” definition, 361 

Cementing of tubes in fuzes, 252 
Cements 

for anchoring fuze parts, 206 
for fuze oscillators, 248 
Cenco rocket, 326-327 
Centrifuge for large fuzes, 298 
Ceramic amplifiers, 259 
Ceramic oscillator .blocks, 250, 253-256 
assembly, 256 
construction, 253 
electrical properties, 253 
mechanical properties, 253 
metalizing, 254 
resistoring, 255 

soldering to ceramic surfaces, 255 
Chemical-bomb fuzes, 3 
Chemical- warfare spray tank, 10 
CIMA fuzes, performance, 418-419 
Clock mechanism for arming fuzes, 170, 
192 

Construction of proximity fuzes 
see Mechanical design of fuzes 
Contact-burst bombs, compared with 
air-burst bombs, 414 
Copper oxide rectifiers, 154-155 
Critical voltage, definition, 286 

Dashpot arming device for fuzes, 192 
Definitions, 211 
Detector circuit, 43-44 
Detonation of fuzes, 213 
impact detonation, 175 
in-line detonators, 169 
Detonator circuit, 117-131 
capacitor, 120-122 
detonator, 118-120 
electric (RC) arming, 125-130 
firing system, 155-156 
operation, 124-125 
requirements, 117-118 
safety features, 130-131 
self-destruction, 131 
tetryl booster, 118 
thyratron, 122-124 
time lags, 119-120 

Developmental relations among fuzes, 
210-211 


/ 


INDEX 


471 


Diode tube tests, 291 
Dipole 

see Antenna 

Directivity patterns, 43-50 
errors due to ground reflection, 77-S0 
measurement, 43-45 
reflections from ground, 44-45 
space radiation pattern, 25 
Directivity patterns, longitudinal ex- 
citation, 45-48 

comparison of patterns, 47-48 
general features, 46-47 
typical patterns, 45-46 
Directivity patterns, transverse excita- 
tion, 48-50 

loop excitation, 49-50 
transverse dipole, 48-49 
Dive bombing tests, VT fuzed bombs, 
323 

“Dog collar’’ construction of amplifier, 
259 

Doppler frequency 

antenna impedance, 18 
reflected impedance, 33 
Doppler fuzes, 4-9 

operation and principal components, 
5-9 

optimum burst height, 7-8 
Douglas Aircraft Company, nozzles for 
fuzes, 200 

Dow potting materials, 208 
Dow Q247 plastic for fuzes, 205, 206 
Dynamic balancing of proximity fuzes, 
168, 201-203 

Dynamic torque tests, 299 

Early functioning 
see Afterburning 

Effective critical voltage, definition, 286 
Electronic systems, 81-166 
amplifier, 103-117 
detonator circuit, 117-131 
power supplies, 131-157 
radio-frequency unit, 81-103 
Electronic systems, coordination, 157- 
166 

battery-powered rocket fuze, 158-160 
generator-powered bomb fuze, bar 
type, 164-165 

generator-powered bomb fuze, ring 
type, 160-164 

generator - powered trench - mortar 
shell fuzes, 165-166 

Field testing, 312-359 
bomb fuzes, 313-324 
mortar shell fuzes, 340-359 
procedure and equipment, 312-313 
purpose, 312 
rocket fuzes, 324-340 
Filter condensers for proximity fuzes, 27 0 


5.0 Navy rocket fuze 
see AR 5.0 Navy rocket fuze 
FOMA fuzes, performance, 418-419 
4.5-in. Army rocket fuzes, 213-217, 
363-376 

see also T-5 fuze; T-6 fuze 
afterburning, 364-366 
amplifier, 217 
arming mechanism, 216 
arrangement of components, 216 
ground-to-ground firing, 216 
limitation, 213 
middle functioning, 366-367 
military requirements, 213 
plane-to-ground firing, 216 
plane-to-plane firing, 215 
radiation pattern, 238 
rain effect, 368 
r-f system, 217 
safety and arming, 214 
scoring methods, 363-364 
self-destruction, 215 
spin effect on arming, 368 
sympathetic functioning, 367-368 
Fragmentation bomb fuzes, military 
requirements, 3 

F ragmentation effect of air-burst bombs, 
412-414 

Fuze nomenclature, summary, 362 
Fuze operation in flight, 319-321 
generator speed, 320-321 
mechanical trouble, 319-320 
observational procedure, 319 

Gain-control condensers for amplifiers, 
261 

Gas bombs, effectiveness, 416 
Gauging tests, 300, 310 
Generator 

production testing, 303-305 
speed, bomb fuze in flight, 320-321 
speed, mortar shell fuzes, 351 
storage systems, 134-135 
testing, 294-295 

Generator, construction, 267-270 
bearings, 268 
coil construction, 268 
housing, 267 
rotors, 269 
shafts, 269 

stator impregnation, 269 
Generator, mechanically-driven rotary, 
134 

Generator, wind-driven, 135-136, 140- 
153 

alternator, 146-147 
bearings, 144-145 
dynamic balancing, 145 
electric design, 145-150 
nose-mounted vane, 140 
operating range, 141 



production models, 150-153 
rotor, 148-150 
single serpentine coil, 151 
six-coil generator, 150-151 
vane and turbine, 141-144 
voltage regulation, 147-148 
Generator-powered fuzes, 160-165, 177- 
186 

amplifier requirements, 162-163 
antenna design, 162 
arming, 164 

bomb fuze, bar-type, 164-165 
bomb fuze, ring-type, 160-164 
carrier frequency, 161-162 
feedback amplifier circuit, 111 
miniature fuzes for trench mortars 
and rockets, 188-198 
oscillator-diode circuit, 162 
overall stability, 164 
power supply, 163 

RRLG fuze for rocket application, 
177-178 

size and location, 161 
specific models, 179-188 
trench-mortar, 165-166 
Glidden PT1 and PT2 used for potting 
fuzes, 208 

Glider bomb fuzes, military require- 
ments, 2-3 

Globe-Union Company 

arming mechanisms for battery fuzes, 
177 

ceramic oscillator blocks, 253-256 
T-132 fuze, 189-193, 241-244, 417- 
419 

GP (general-purpose) bomb fuze, mili- 
tary requirements, 2-3 
Ground-approach fuzes 

amplifier characteristics, 106-110 
antenna impedance, 23-24, 50-54 
reflected impedance, 28 
summary of characteristics, 10-13 

HC (high-capacity) bombs, British, 
415-416 

Humidity tests, 297-298 
HVAR rocket, characteristics, 326 

IE-28 test set, 298 

Impact detonation of proximity fuzes, 
175 

Impedance, mutual, radiation field, 24- 
27 

antenna gain, 26 

between two arbitrary antennas, 26- 
27 

field equations for arbitrary antenna, 
25-26 

Impedance, reflected, 27-34 
airborne target equation, 28-30 
general properties, 33-34 


472 


INDEX 


ground interference, 30 
ground-approach equation, 28 
transverse antenna fuze, 30-32 
Impedance antenna 
see Antenna impedance 
Impedance signal, 51-54, 59-61 
see also Signal simulators 
ballistic and target factors, 53-54 
fuze antenna factors, 51-52 
wave amplitude, 60-61 
wave phase, 59-60 

Inertia arming of proximity fuzes, 171- 
174 

In-line detonators for proximity fuzes, 
169 

Jamming fuzes, antenna impedance, 24 
Jolt test for fuzes, 191, 297 

Katrinka bomb fuzes, 198 

Laboratory tests, 278-311 
audio portions, 284-287 
complete units, 295-296 
component testing, 290-295 
gauging, 300 

mechanical tests, 298-300 
overall test, 278 

pilot production test line, 300-308 
procedure, 278 
purpose of tests, 278 
quality control testing, 308-311 
radio-frequency sections, 278-284 
service tests, 297-298 
stability, 287-290 
Launchers for rocket testing, 327 
LC (light-case) bomb fuze, military 
requirements, 2-3 

Loading devices for fuze testing, 280-283 
Loading requirements of fuzes, 279-280 
Longitudinally excited proximity fuze, 
167 

Lucite fuze caps, rain protection device, 
368 

M-2 electric detonator, 119 
M-8 rocket fuze 
see T-5 fuze 

M-10 chemical warfare spray tank, 415 
M-64 air-burst bomb, effectiveness, 
412-416 

M-81 air-burst bomb, effectiveness, 
412-416 
M-166 fuze 
see T-51 fuze 
M-168 bomb fuze, 229 
Manual arming of proximity fuzes, 169 
MC-382 rocket fuze 
early functioning, 371 
radiating system, 89 
tube characteristics, 92 


Mechanical design of fuzes, 167-208 
arrangement of main components, 
167 

battery fuzes, 175-177 
choice of plastics, 204-208 
dynamic balancing, 201-203 
experimental fuzes, 198-199 
general requirements, 167-168 
generator fuzes for rockets and bombs, 
177-188 

miniature fuzes for trench mortars 
and rockets, 188-198 
mounting of fuzes into missiles, 199- 
200 

rigidity, 168 

safety and arming, 168 

size, 168 

speed regulation for windmills and 
turbines, 200-201 

“Michigan sensitivity” of a fuze, 64, 83 
“Micro-Dynetric” balancing of fuze, 
203 

Military requirements, 1-4 
arming and safety requirements, 2 
functioning point, 1 
mechanical features, 1-2 
MinSAT (minimum safe air-travel-to- 
arming), 222-223, 389-390 
Mk-171 fuze 
see T-30 fuze 
Mk-172 fuze 
see T-2004 fuze 

Monsanto Styramic 18, plastic mate- 
rial for fuzes, 205 

Mortar shell fuzes, 188-197, 340-359 
see also T-132 fuze; T-171 fuze; T-172 
fuze 

arming, 418-419 

breech-loading mortar recovery, 359 
dynamic balancing, 202 
electronic system, 165-166 
firing coordination, 342-343 
fuze flight performance, 350-351 
gun position, 344-346 
height of function, 350, 353-356 
loading operations, 343-344 
mortar shell trajectories, 352-353 
packaging tests, 417-418 
performance under standard condi- 
tions, 416-417 
ranges, 419-420 
safety in arming, 171 
test measurements, 346-350 
weather effects, 351-352 
Mortar shell retrieving devices, 355-357 
Mortar shell trajectory calculation, 
352-353 

Mounting of fuzes into missiles, 199- 
200 

Mustard gas air-burst bombs, 416 


Napalm-gasoline gel, fire bombing use, 
414-415 

National Bureau of Standards 

acceleration integrator for arming 
fuzes, 171-174 

bearings for T-132 and T-171 fuzes, 
190 

centrifuges for fuze tests, 177, 188 
dipoles for fuzes, 184 
fuze battery, 133-134 
gear train, 186 
T-12 fuze, 177-178 
T-171 fuze, 188-195, 241-244, 418-419 
testing equipment for proximity 
fuzes, 275 

Navy rocket fuzes, 377-386 
see also AR 5.0 Navy rocket fuze; 

T-30 fuze; T-2004 fuze 
acceptance testing requirements, 430- 
431 

arming distances, 378-379 
dumping, 379 
general discussion, 377 
mechanical arming, 377-378 
pulsing tests, 378-379 
safety tests, 380 
Noise antenna, 71-75 
Noise sources in fuzes, 287-290 
Nomograph for use in mortar shell test- 
ing, 348-349 

Normal critical voltage, definition, 286 
Nose assembly of proximity fuzes, 265- 
266 

Nose fuzes 

see T-50 fuze; T-51 fuze 
NR-3A Raytheon tube, characteristics, 
92-93 

NS-3 Sylvania tube, characteristics, 92 

OD (oscillator-diode) fuzes, 100 
Oscillators, 247-256 
carrier frequency uniformity, 250 
ceramic blocks, 250, 253-256 
coil construction, 250-252 
design, 88-89 
metalizing of blocks, 254 
power oscillating detector, 84-85 
“printed” circuits, 250 
production plant testing, 302 
production procedures, 247-253 
reaction grid detector, 84, 98 
requirements, 247 
thermoplastic blocks, 248 
thermosetting phenolic blocks, 248 
tube mounting, 252 
types of construction, 248 

P-4 bomb fuze, generator design, 141, 
153 

P-4 771B bomb fuze, 199 
Packaging tests, 297 


INDEX 


473 


Parachute recovery devices for VT 
mortar fuzes, 355-359 
Passive fuzes, 5 

PD M-4 fuzes, comparison with T-6 
fuze, 376 

Pellets for elimination of afterburning 
in rocket propellants, 365-366 
Perchloric acid battery cell, 139 
Performance terminology for fuzes, 211 
Phenolic thermosetting oscillator 
blocks, 248 

Photographic observations 
detonation of VT mortar shells, 353- 
356 

in bomb fuze testing, 317-318 
Pilot plant production of fuzes, 245 
Pilot production test line, 300-308 
audio prepot and postpot test posi- 
tions, 303-304 

audio pretest position, 302-303 
generator test position, 303-305 
head test position, 303 
oscillator pretest position, 302 
performance testing, final, 306-307 
power supply test position, 306 
pulse test, 307-308 
rectifier-filter test position, 305-306 
Piton-Bressant method, mortar shell 
trajectory calculations, 352-353 
Plastics for fuzes, 204-208 
basic requirements, 204 
cementing, 206 
solder flux, 208 
thermoplastic materials, 204 
POD (power oscillating detector), 82, 
84-85 

Pole-test measurement of fuze sensi- 
tivity, 65, 87 

Potting of amplifiers, 261-265 

as part of the production line, 264 
Glidden compound, 265 
immersion in hot waxes, 262 
in the fuze cavities, 263 
ingredients, 263 
tung oil mixtures, 264 
vacuum potting, 264 
Potting of fuzes, 207-208, 253 
Powder train interrupters, 168 
Power oscillating detector, 82, 84-85 
Power radiation pattern of fuze antenna 
see Directivity patterns 
Power supplies, 131-157, 266-272 
dry batteries, 133, 136-138 
electric components, 270-272 
filter and detonator firing system, 
155-156 

filter condenser, 270 
generator, 134-136, 267-270 
production testing, 306 
rectifiers, 153-155, 271 
requirements, 131-133, 267 


reserve batteries, 133-134, 138-140 
supply circuits, 156-157 
survey of possible sources, 133-136 
testing, 294-295, 306 
types, 266 

wind-driven generators, 140-153 
Production of fuzes, 227-239, 245-277 
achievement, 277 
amplifiers, 256-265 
assembly line, 275 
bar-type fuzes, 228 
nose assembly, 265-266 
organization and planning, 245-247 
oscillators, 247-256 
pilot plant, 245 

power supply and arming, 266-272 
process flow chart, 246 
production techniques, 272-275 
ring-type fuzes, 228 
soldering, 272 
testing, 275-277, 300-308 
VT bomb fuzes, 228 
Proper function of a fuze, definition, 211 
Proximity fuzes 
effectiveness, 11-16 
electronic systems, 81-166 
field testing, 312-359 
laboratory tests, 278-311 
mechanical design, 167-208 
military requirements and objectives, 
1-4 

performance, 360-432 
production, 227-239, 245-277 
radiation interaction system, 17-80 
Proximity fuzes, types 

see also Bomb fuzes; Rocket fuzes 
active fuzes, 4-5 
bar-type fuze, 221-228, 405-412 
battery fuzes, 175-177 
doppler fuzes, 4-9 

generator-powered fuzes, 160-165, 
177-186 

mortar shell fuzes, 188-197, 241-244, 
340-359, 416-420 

ring-type fuzes, 223-229, 394-405 
Pulse test, 296, 307-308 
“Purge pellets” for use in rocket propel- 
lants, 365-366 

Quality control testing, 308-311 

comparison with pilot production 
testing, 308-309 
procedure, 309 
specific tests, 310-311 

Radiating system, 89-90 
Radiation resistance 

effect of feed geometry, 39-40 
effect on reflected impedance, 33 
experimental measurement, 38-39 
typical values, 41-43 


Radiation theory, 17-80 
antenna impedance, 17-22, 37-43 
antenna noise, 71-75 
circuit response to antenna imped- 
ance modulation, 34-37 
directivity patterns, 43-50, 77-80 
evaluation of antenna constant, 75- 
77 

mutual impedance, 24-27 
reflected impedance, 27-34 
signal simulation, 64-71 
two-terminal networks, 22-24 
working signals, airborne target, 59- 
64 

working signals, ground-approach 
case, 50-54 

Radiation theory, induction field, 54-59 
effect on function heights, 57-59 
second approximation to the field 
equations, 55-57 
Radio proximity fuzes 
see Proximity fuzes 

Radio rocket longitudinal generator 
(RRLG), 177-178 
Radio-frequency system, 81-103 
carrier frequency, 284 
loading devices, 280-283 
loading requirements, 279-280 
oscillator design, 88-89 
power oscillating detector, 82 
radiating system, 89-90 
reaction grid detector, 82 
requirements, 81-82 
sensitivity, 82-89, 102-103, 283 
shielding of fuzes, 280 
spurious signals and circuit stability, 
95-100 

stability, 283 
tests, 278-284 
tube characteristics, 90-95 
typical designs, 100-102 
Radio-frequency system, signal simu- 
lators 
field, 65 

laboratory, 65-69 

resistance component simulators, 66- 
68 

rotating vector simulators, 68-69 
Radius of action (ROA) of fuzes, defini- 
tion, 211 

Rain 

effect on rocket fuzes, 337, 368 
protection with Lucite fuze caps, 368 
Random function of a fuze, definition, 
211 

Rate of spin, rocket, 340 
Raymond Engineering Laboratories, 
clock rotor for fuzes, 192 
RC arming, 125-129 
dumping, 128-129 
measurement, 335 


474 


INDEX 


pulse protection, 129 
testing, 296 

Reactance across antenna terminals 
effect of feed geometry, 39-40 
measurement, 39 
typical values, 41-43 
Reaction grid detector 
circuit characteristics, 93 
design, 88-89 
dynamic stability, 98 
performance compared with idealiza- 
tion, 84 

suggested antimicrophony circuit, 99 
tuning effects, 100-101 
Recordak viewers, use in bomb fuze 
testing, 317-318, 320 
Rectifier system 

blocking layer rectifiers, 154-155 
filters, production testing, 305-306 
for proximity fuzes, 271-272 
testing, 293-294 
vacuum-tube rectifiers, 154 
Reflection 

see Radiation theory 
Resistance component signal simu- 
lators, 66-68 
diode, 67-68 
dipole reflectors, 66-67 
dummy antenna, 66 
thermistors, 68 
triode, 68 

Resistors, compensated, 281-283 
R-f system 

see Radio-frequency system 
RGD oscillator 

see Reaction grid detector 
Rigidity of proximity fuzes, 168 
Ring construction of amplifiers, 259 
Ring-type bomb fuzes, 223-229, 394-405 
see also T-60 fuze 
amplifier, 226 

arming devices, delayed, 402-403 
brown carrier, 228, 229 
burst heights, 224, 396, 398-399, 403- 
405 

comparison with bar-type fuzes, 221 
effect of release altitude, 401, 403-404 
effect of train release, 404-405 
effect of train spacing, 401 
effect of vehicle size, 400, 404 
fin insulators, 402, 404 
fin thickness, 402, 403-404 
fuze protective devices, 401-402 
production data, 229, 232 
reliability, 223 
washers, 401 
white carrier, 228, 232 
Ring-type bomb fuzes, acceptance tests, 
394-405 

burst height distribution character- 
istics, 398-399 


conditions for acceptance, 394 
effect of test conditions on perform- 
ance, 395-396 
mean burst heights, 396 
metal parts, 395 
summary, 399-400 
T-50-E1 fuze, 396-397 
T-50-E4 fuze, 398 
T-89 fuze, 396-397 
T-90 fuze, 398 
T-91 fuze, 397 
T-91-E1 fuze, 397-398 
T-92-E1 fuze, 398 
Ring-type rocket fuzes 
see AR 5.0 Navy locket fuze; T-30 
fuze 

ROA (radius of action) of fuzes, 211 
Rocket ballistics 
angle of approach, 339-340 
rate of spin, 340 
velocity and acceleration, 339 
yaw, 340 

Rocket fuzes, 235-241, 324-340 
see also AR 5.0 Navy rocket fuze; 

4.5-in. Army rocket fuzes 
arming, 159-160, 333-335 
ballistics of rockets, 339-340 
carrier performance, 331-332 
effect of propellant temperature, 336 
effect of raindrops, 337-339 
fin structure, 336 
firing from airplane, 331 
high-angle firing, 331 
horizontal firing, 329-331 
metal vanes, 143 
ring-type, 235 

rocket characteristics, 326-328 
safety in arming, 171 
sensitivity and burst surface, 332-333 
sensitivity requirements, 6-7, 63-64 
sympathetic functioning, 339 
testing procedure and equipment, 
324-326 

water-approach tests, 332-333 
Rocket fuzes, afterburning in 
Ballistite burning, 364-365 
burning process, 364-365 
definition, 211 

pellets added to Ballistite, 365 
summary, 336 

trap ring variations, 365-366 
with various propellants, 337 
Rocket fuzes, battery-powered 
amplifier requirements, 159 
arming, 159-160 
carrier frequency, 158-159 
mechanical stability, 160 
oscillator and detector, 159 
power supply, 159 ^ 

size and location, 158 * 



Rocket fuzes, specific models 

see also T-5 fuze; T-6 fuze; T-12 fuze; 
T-30 fuze; T-2004 fuze; T-2005 
fuze 

Rotating vector signal simulators, 68- 
69 

Rotors for fuze generators, 269 
RRLG fuze, 177-178 

Safety requirements, 168-175 
see also Arming methods 
comparison of proximity fuzes with 
other fuzes, 168 
for detonator circuit, 130-131 
for 4.5-in. Army rocket fuzes, 214 
impact detonation, 175 
powder train interrupters, 168 
rotating and nonrotating projectiles, 
169 

self-destruction, 174 
Salt spray tests, 298 
Sandwich construction of amplifiers, 
257 

Selenium rectifiers, 154-155, 271-272, 
274 

Self destruction (SD) mechanism of 
fuzes, 131, 174, 215, 296 
Sensitivity of fuze, 82-89 
definition, 82-87 
directional sensitivity, 6-7 
experimental determination, 87-88 
“Michigan sensitivity,” 64, 83 
pole-test measurement, 65, 87 
radio-frequency sections, 283 
rocket fuze sensitivity, 63-64, 332- 
333 

sensitivity concept, 102-103 
Signal simulators, 64-71 
field r-f simulator, 65 
laboratory audio simulator, 69-70 
laboratory r-f simulators, 65-69 
overall signal simulator, 71 
required properties, 64-65 
Signals, fuze 
differential, 34-35 
finite, 35 

Signals, spurious, 95-100 

antimicrophony circuits, 98-99 
arming pulse, 99 
component noise, 95-96 
corona effects, 96 
response of amplifier, 115-116 
unstable oscillation, 96-98 
Size of proximity fuzes, 168 
Solar Aircraft Company, doughnut 
arming mechanism, 188 
Soldering 

ceramic surfaces, 255 
flux for proximity fuzes, 208 
techniques, 272-273 

Spin effect on arming, rocket fuzes, 368 


INDEX 


475 


Stability tests 
noise sources in fuzes, 289 
purpose, 287 

radio-frequency sections, 283 
vibration and shock production, 287- 
289 

Static torque tests, 299 
Styramic 18, plastic for fuzes, 206 
Sympathetic functioning 
“of a fuze, definition, 211 
of rocket fuzes, 339 

T-2 arming delay device, 170, 322 
T-5 fuze 

see also 4.5-in. Army rocket fuzes 
acceptance tests, 370-371, 431-432 
amplifier, 217 
applications, 213 
arming, 173, 368-370 
burst heights, 238, 373-375 
casualties as function of burst height, 
373-375 

dimensions, 158 

effect of distance to target, 371-372 
effect of trajectory dispersion on 
burst distribution, 372-373 
limitation, 214 
military requirements, 2 
operational use, 420-422, 427 
oscillator, 217 

plane-to-ground firing, 216, 372-375 
plane-to-plane firing, 215, 372 
plastic content, 204 
premature functioning, 369-370 
risk of random bursts, 215 
self destruction, 131, 174, 215, 217 
tests, 327 

zero shielding, 372-375 
T-6 fuze 

see also 4.5-in. Army rocket fuzes 
amplifier, 217 
application, 213 
arming, 375-376 
burst heights, 238 

comparison with PD M-4 fuzes, 376 
general description, 10 
ground-to-ground firing, 216 
impact detonator, 175 
operational use, 420-422, 427 
oscillator, 217 
performance, summary, 13 
probability of arming within certain 
distance, 215 
reliability, 376 
T-12 fuze, 10, 177-178 
T-30 fuze, 240-241, 377-384 
afterburning, 380-382 
arming, 186, 240-241, 377-379 
characteristics, 241 
compensated resistor tests, 281 
effect of propellant characteristics, 380 


function on approach to water, 382- 
383 

gear train, 186 
ground-launched tests, 381 
metal vane, 143 
mock-plane tests, 383 
plane firing, 381 
plane-to-drone firing, 383-384 
plane-to-water firing, 382-383 
potting the amplifier, 262 
power supply, 156-157 
static tests in an airstream, 380-381 
T-40 fuze, 3, 198 
T-43 fuze, 3, 198 
T-50 fuze, 179-184 
adapter case, 179 
air travel, 183 
antenna, 89, 180 
arming, 181-184 
coupling, 180 
design, 179-181 
detonation, 183 
dynamic balancing, 202 
oscillator-diode circuit, 100 
plastic content, 204 
power supply, 156 
reactor grid detector circuit, 101 
self-destruction, 181 
use in air-burst bombs, 412-416 
vanes, 179 
windmills, 179-180 
T-50-E1 fuze 

characteristics, 229 
general description, 10 
operational use, 421-423 
performance, 13 
plastic vane, 142 
tests, 396-397 
T-50-E4 fuze 

characteristics, 232 
general description, 10 
operational use, 422-426 
performance, 13 
tests, 398 
T-51 fuze 

electronic design, 164-165 
feedback amplifier, 112 
general description, 10-11, 184 
generator, 140 
performance, 13 
plastic content, 205 
plastic vane, 142-143 
power supply, 156 
radiation resistance, 41 
release, 408 
RGD circuit, 101 
use in air-burst bombs, 412-416 
use in mustard gas bomb, 416 
T-51-E1 fuze 

characteristics, 234 
operational use, 422-426 


SECRET 


performance in train, 410 
release, 409 
T-74 rocket, fins, 328 
T-82 fuze 

amplifier construction, 258 
flexible blades for turbines, 201 
general description, 11, 239-240 
generator design, 152-153 
mechanical design, 184-186 
power supply, 158 
release, 408, 409 
turbine, 143-144 
turbo-generator, 141 
T-83 rocket, characteristics, 326 
T-89 fuze 

characteristics, 229 
general description, 10 
performance, 13 
tests, 396-397 
T-90 fuze 

characteristics, 232 
performance, 13 
tests, 398 
T-91 fuze 

characteristics, 229 
general description, 10 
performance, 13 
tests, 397 

T-91-E1 fuze, tests, 397-398 
T-92 fuze 

characteristics, 232 
general description, 10 
performance, 13 
T-92-E1 fuze 

characteristics, 232 
tests, 398 

T-132 fuze, 187-195, 241-244 
arming, 99, 169, 174, 190-192 
arrangement of components, 189 
dashpot arming device, 192 
detonator rotor, 191 
dynamic balancing, 190 
electronic assembly, 193 
end cap design, 89 
features summarized, 242 
general description, 11 
generator design, 141, 151 
generators, 189 
jolt test, 191 

military requirements, 3-4 
oscillator, 253-256 
overall dimensions, 193 
performance, 417-418 
plastic content, 205 
power supply, 157 
turbine, 144 

T-171 fuze, 188-195, 241-244 
arming, 99, 126, 191-192 
arrangement of components, 189 
detonator rotor, 191 
dynamic balancing, 190 


1 


476 


INDEX 


end cap design, 89 
generator design, 141, 151 
generators, 189 
jolt test, 191 

military requirements, 3-4 
overall dimensions, 193 
performance, 418-419 
plastic content, 205 
potting, 207-208 
power supply, 157 
T-172 fuze, 195-197, 241-244 
antenna, 165 
general description, 11 
generator design, 141, 151-152, 196 
mechanical design, 195 
military requirements, 3-4 
nozzles for speed regulation, 200 
oscillator circuit, 101-102 
overall dimensions, 195 
power supply, 157 
T-712 bomb fuze, 234 
T-2004 fuze 

see also AR 5.0 Navy rocket fuze 
acceptance tests, 385-386, 430-431 
arming, 186, 219, 377-379 
burst heights, 386 
gear train, 186 
general description, 11 
high-angle firing, 384 
metal vane, 143 
performance, 13 
plane-to-surface firing, 385 
power supply, 156-157 
T-2005 fuze 
arming system, 197 
general description, 11 
generator design, 141 
generator power supply, 197 
plastic content, 206 
self-destruction, 198 
specification requirements, 241 
Tail fuzes, 3, 198 

Target, effect on impedance signal, 53- 
54 

Targets for proximity fuzes, 1 
Telescope, battery command, 345 
Temperature tests, 297 
Tetryl in VT mortar fuzes, detonation, 
353-356 

Thermistor signal simulator, 68 
Thermoplastic materials for proximity 
fuzes, 204 

Thermoplastic oscillator blocks, 248 


Thermosetting phenolic oscillator 
blocks, 248 

Thyratron in detonator circuit 
grid voltage, 122-123 
leakage and grid current, 123 
life, 123-124 

low power consumption, 122 
microphonics, 123 
stability, 123 
surge characteristics, 123 
Thyratron tests, 286-287, 293 
Timing devices used in arming prox- 
imity fuzes, 170 

Train bombing tests, VT-fuzed bombs, 
322-323 

Transverse-antenna fuzes, 112-113 
Trench mortar fuzes 

gain-frequency characteristic curve, 
110 

generator-powered, 165-166 
T-132; 11, 187-195, 241-244 
T-171; 11, 188-195, 241-244 
T-172; 11, 195-197, 241-244 
Tube characteristics, 90-95 
diodes, 95 

microphonics, 94-95 
NR-3A Raytheon, 92-93 
NS-3 Sylvania, 92 
pentodes, 114-115 

requirements and restrictions, 90-92 

ruggedness, 95 

self-noise, 94 

testing, 290-292 

triodes, 92-95 

University of California 

bearings for T-132 and T-171 fuzes, 
190 

centrifugal speed regulation for fuzes, 
201 

nozzles for fuzes, 200 
University of Florida, T-172 fuze, 195 
University of Iowa, mortar shell fuze 
testing, 340-359 
Uskon cloth, 281 


Vacuum potting of amplifiers, 264 
Vane shaft bearings for proximity fuze 
noses, 265 

Vibration tests, 297 

Vibrators for fuze testing, 287-290 


VT fuzes, 360-432 

see also AR 5.0 Navy rocket fuze; 

4.5-in. Army rocket fuzes 
Army operational use, 420-423 
conclusions from service use, 427-428 
data sources, 360-363 
for 4.5-in. Army rockets, 363-376 
for Navy rockets, 377-380 
mortar shell fuzes, 353-356, 416-420 
Navy operational use, 423-427 
performance analysis methods, 360- 
363 

proximity bursts, 215 
research recommendations, 427-428 
safety and arming, 212 
summary, 428 

VT-fuzed bombs, tests, 220-227, 386-416 
acceptance testing requirements, 428- 
430 

arming tests, 321-322 
burst heights, 224 
dive bombing tests, 323 
production data, 228 
train bombing tests, 322-323 

Wafer construction of amplifiers, 257 
Washers for bomb fuzes, 401 
Water-approach tests, rockets, 332-333 
Waxes for potting of amplifiers, 262 
Westinghouse Electric Corporation 
dynamic balancing of fuzes, 202 
power oscillating detector, 82 
T-82 bomb fuze, 184-186 
White carrier bomb fuzes 
amplifier gain, 232 
burst heights, 232, 233 
performance, 400 
radiation patterns, 233 
T-82 fuze, 239-240 
Wind-driven generators 
see Generator, wind-driven 
Wurlitzer Company 
generator for T-132 fuze, 189 
T-12 fuze, 177-178 

Yaw of a rocket, 340 

Yellow carrier bomb fuzes, 234-235 

Zenith Radio Corporation 
dipoles for fuzes, 184 
generator for T-172 fuze, 196 
potting material, 207 
“Zero shielding” of T-5 fuze, 372-375 


ssssS 5, 



DECLA SSIFIED 
By authority Secretary of 

SEP 1 1960 


Defense memo 2 August 1960 
UBRARY OF CONGRESS 










DECLASS I FIED 
By authority Secretary of 

c 3 11960 

Defense memo 2 August 1960 
LIBRARY OF CONGRESS 


..declassified 

By aulh >*etary of 









Defens 


i960 


2SS 


LIBRA, 






